Show message on login screen when user's group/role has been deleted.

- Changed login screen to show message when trying to login with userid that does not have role or group associated with it or their role/group might have been deleted from database.
- Changed group details screen to not try to show role details of group when group's role has been deleted.
- Fixed/Added spec tests around new changes.

https://bugzilla.redhat.com/show_bug.cgi?id=1090901
Merge pull request #351 from h-kataria/user_with_no_role_or_group

Show message on login screen when user's group/role has been deleted.