webadmin: Fixed message when adding Posix domain when not supported

The message when adding a Posix domain when it's not supported on the
cluster was broken and lacking the action type and entity type

Change-Id: I237e40dd325c7b36c4413eab48e3aed41c090c4f
Bug-Url: https://bugzilla.redhat.com/1074254
Signed-off-by: Tal Nisan <tnisan@redhat.com>