Description of problem:
Issuing a PUT request to the /users/:id API path will fail if the request includes the `auth_source_ldap` parameter. The API doc states that this parameter is acceptable, but the application returns an HTTP 500 error with this message:

    auth_source_id is not allowed as nested parameter for users. Allowed parameters are auth_source_ldap_id, role_id, location_id, organization_id, usergroup_id

Version-Release number of selected component (if applicable):
Tested against a nightly build of Satellite 6 with the following packages installed:

* apr-util-ldap-1.3.9-3.el6_0.1.x86_64
* candlepin-0.9.32-1.el6.noarch
* candlepin-common-1.0.8-1.el6.noarch
* candlepin-selinux-0.9.32-1.el6.noarch
* candlepin-tomcat6-0.9.32-1.el6.noarch
* elasticsearch-0.90.10-7.el6.noarch
* foreman-1.7.0-0.develop.201410171840git6be0508.el6.noarch
* foreman-compute-1.7.0-0.develop.201410171840git6be0508.el6.noarch
* foreman-gce-1.7.0-0.develop.201410171840git6be0508.el6.noarch
* foreman-libvirt-1.7.0-0.develop.201410171840git6be0508.el6.noarch
* foreman-ovirt-1.7.0-0.develop.201410171840git6be0508.el6.noarch
* foreman-postgresql-1.7.0-0.develop.201410171840git6be0508.el6.noarch
* foreman-proxy-1.7.0-0.develop.201410170812git8aa4e0f.el6.noarch
* foreman-release-1.7.0-0.develop.201410171840git6be0508.el6.noarch
* foreman-selinux-1.7.0-0.develop.201409301113git2f345de.el6.noarch
* foreman-vmware-1.7.0-0.develop.201410171840git6be0508.el6.noarch
* katello-2.1.0-1.201410191445gitf0d0a33.el6.noarch
* katello-certs-tools-2.0.1-1.el6.noarch
* katello-default-ca-1.0-1.noarch
* katello-installer-2.1.0-1.201410162242git33b9fc3.el6.noarch
* katello-repos-2.1.1-1.el6.noarch
* katello-server-ca-1.0-1.noarch
* openldap-2.4.23-32.el6_4.1.x86_64
* pulp-docker-plugins-0.2.1-0.2.beta.el6.noarch
* pulp-katello-0.3-3.el6.noarch
* pulp-nodes-common-2.5.0-0.7.beta.el6.noarch
* pulp-nodes-parent-2.5.0-0.7.beta.el6.noarch
* pulp-puppet-plugins-2.5.0-0.7.beta.el6.noarch
* pulp-puppet-tools-2.5.0-0.7.beta.el6.noarch
* pulp-rpm-plugins-2.5.0-0.7.beta.el6.noarch
* pulp-selinux-2.5.0-0.7.beta.el6.noarch
* pulp-server-2.5.0-0.7.beta.el6.noarch
* python-ldap-2.3.10-1.el6.x86_64
* ruby193-rubygem-ldap_fluff-0.3.2-1.el6.noarch
* ruby193-rubygem-net-ldap-0.3.1-2.el6.noarch
* ruby193-rubygem-runcible-1.2.0-1.el6.noarch

How reproducible:
100%

Steps to Reproduce:
See the "Description of problem" section at the top of this message.

Actual results:
An HTTP 200 response and a properly updated user.

Expected results:
An HTTP 500 response and an unchanged user.

Additional info:
Here's a snippet from the server log:

    Processing by Api::V2::UsersController#update as JSON
      Parameters: {
        "mail"=>"JgUTagrX",
        "login"=>"g",
        "password"=>"[FILTERED]",
        "auth_source_id"=>1,
        "apiv"=>"v2",
        "id"=>"51",
        "user"=>{
          "login"=>"g",
          "mail"=>"JgUTagrX",
          "auth_source_id"=>1,
          "password"=>"[FILTERED]"
        }
      }
    Authorized user admin(Admin User)
    auth_source_id is not allowed as nested parameter for users. Allowed parameters are auth_source_ldap_id, role_id, location_id, organization_id, usergroup_id (RuntimeError)