Description of problem:
 read-children-names operation is behaving inconsistently on /host=master/server node. On every other existing node this operation returns empty list, but if I stop every server in domain, and run the operation on 'server' child-type, I get "JBAS014793: No known child type named server" message -> indicating that 'server' is not a known child-type.

Version-Release number of selected component (if applicable):
 EAP 6.3.0.ER2

How reproducible:
 Always

Steps to Reproduce:
 1. Start out-of-box domain and connect to CLI
 2. Run following set of commands to stop and remove all default servers
/host=master/server-config=server-one:stop()
/host=master/server-config=server-two:stop()

/host=master/server-config=server-one:remove()
/host=master/server-config=server-two:remove()
/host=master/server-config=server-three:remove()

 3. Note, that 'server' node is listed among available children types for /host=master node
/host=master:read-children-types
{
    "outcome" => "success",
    "result" => [
        "core-service",
        "interface",
        "jvm",
        "path",
        "server",
        "server-config",
        "system-property"
    ]
}

 4. Run read-children-names operation on 'server' and 'server-config' child-type.

Actual results:
/host=master:read-children-names(child-type=server-config)
{
    "outcome" => "success",
    "result" => []
}
/host=master:read-children-names(child-type=server)
{
    "outcome" => "failed",
    "failure-description" => "JBAS014793: No known child type named server",
    "rolled-back" => true
}

Expected results:
/host=master:read-children-names(child-type=server-config)
{
    "outcome" => "success",
    "result" => []
}
/host=master:read-children-names(child-type=server)
{
    "outcome" => "success",
    "result" => []
}

Additional info:
 We may also update the message in org.jboss.as.controller.ControllerMessages from "No known child type named %s" to "No known child-type named %s"