Currently when the guest agent reports that a virtual machine has a session for an user that isn't registered in the oVirt database, the request to get the sessions fails with error 404 (not found).

This isn't correct because the users reported by the guest agent don't need to be registered in the database, they can be local OS users, for example.

The API should be modified so that in this case it returns just the user name and domain or, at least, so that it doesn't fail.

The exception that appears in the server logs when this happens is the following:

2017-04-10 10:51:48,353 ERROR [org.jboss.resteasy.resteasy_jaxrs.i18n] (default task-30) RESTEASY002010: Failed to execute: javax.ws.rs.WebApplicationException: HTTP 404 Not Found
        at org.ovirt.engine.api.restapi.resource.BaseBackendResource.handleError(BaseBackendResource.java:226) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.BackendResource.getEntity(BackendResource.java:118) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.BackendResource.getEntity(BackendResource.java:98) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.AbstractBackendSubResource.performGet(AbstractBackendSubResource.java:34) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.aaa.BackendUserResource.getUserByNameAndDomain(BackendUserResource.java:77) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.BackendVmSessionsResource.setSessionUser(BackendVmSessionsResource.java:87) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.BackendVmSessionsResource.addLinksIncludingUser(BackendVmSessionsResource.java:59) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.BackendVmSessionsResource.list(BackendVmSessionsResource.java:42) [restapi-jaxrs.jar:]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [rt.jar:1.8.0_121]
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) [rt.jar:1.8.0_121]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [rt.jar:1.8.0_121]
        at java.lang.reflect.Method.invoke(Method.java:498) [rt.jar:1.8.0_121]
        at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:139) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:295) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:249) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.core.ResourceLocatorInvoker.invokeOnTargetObject(ResourceLocatorInvoker.java:138) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:107) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.core.ResourceLocatorInvoker.invokeOnTargetObject(ResourceLocatorInvoker.java:133) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:107) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.core.ResourceLocatorInvoker.invokeOnTargetObject(ResourceLocatorInvoker.java:133) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:101) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:402) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:209) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:221) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51) [resteasy-jaxrs.jar:3.0.19.Final-redhat-1]
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) [jboss-servlet-api_3.1_spec.jar:1.0.0.Final-redhat-1]
        at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:129) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at org.ovirt.engine.api.restapi.invocation.VersionFilter.doFilter(VersionFilter.java:120) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.invocation.VersionFilter.doFilter(VersionFilter.java:68) [restapi-jaxrs.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at org.ovirt.engine.api.restapi.invocation.CurrentFilter.doFilter(CurrentFilter.java:84) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.invocation.CurrentFilter.doFilter(CurrentFilter.java:63) [restapi-jaxrs.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at org.ovirt.engine.core.aaa.filters.RestApiSessionMgmtFilter.doFilter(RestApiSessionMgmtFilter.java:78) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at org.ovirt.engine.core.aaa.filters.EnforceAuthFilter.doFilter(EnforceAuthFilter.java:39) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at org.ovirt.engine.core.aaa.filters.SsoRestApiNegotiationFilter.doFilter(SsoRestApiNegotiationFilter.java:91) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at org.ovirt.engine.core.aaa.filters.SsoRestApiAuthFilter.doFilter(SsoRestApiAuthFilter.java:47) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at org.ovirt.engine.core.aaa.filters.SessionValidationFilter.doFilter(SessionValidationFilter.java:59) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at org.ovirt.engine.core.aaa.filters.RestApiSessionValidationFilter.doFilter(RestApiSessionValidationFilter.java:35) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at org.ovirt.engine.api.restapi.security.CSRFProtectionFilter.doFilter(CSRFProtectionFilter.java:111) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.security.CSRFProtectionFilter.doFilter(CSRFProtectionFilter.java:102) [restapi-jaxrs.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at org.ovirt.engine.api.restapi.security.CORSSupportFilter.doFilter(CORSSupportFilter.java:183) [restapi-jaxrs.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core.jar:1.3.25.Final-redhat-1]
        at io.undertow.security.handlers.AuthenticationConstraintHandler.handleRequest(AuthenticationConstraintHandler.java:51) [undertow-core.jar:1.3.25.Final-redhat-1]
        at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46) [undertow-core.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.security.ServletSecurityConstraintHandler.handleRequest(ServletSecurityConstraintHandler.java:59) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60) [undertow-core.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50) [undertow-core.jar:1.3.25.Final-redhat-1]
        at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43) [undertow-core.jar:1.3.25.Final-redhat-1]
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core.jar:1.3.25.Final-redhat-1]
        at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core.jar:1.3.25.Final-redhat-1]
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:285) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:264) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:175) [undertow-servlet.jar:1.3.25.Final-redhat-1]
        at io.undertow.server.Connectors.executeRootHandler(Connectors.java:207) [undertow-core.jar:1.3.25.Final-redhat-1]
        at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:802) [undertow-core.jar:1.3.25.Final-redhat-1]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [rt.jar:1.8.0_121]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [rt.jar:1.8.0_121]
        at java.lang.Thread.run(Thread.java:745) [rt.jar:1.8.0_121]