Add detection for users from trusted/invalid realms
When user from other realm than FreeIPA's tries to use Web UI
(login via forms-based auth or with valid trusted realm ticket),
the 401 Unauthorized error with X-Ipa-Rejection-Reason=denied
is returned.
Also, the support for usernames of the form user@SERVER.REALM
or user@server.realm was added.
https://fedorahosted.org/freeipa/ticket/3252