Decouple user limit from guest creation

Allow Guest to be created even if there are N users.
Allow N users to be created even if there are N-1 users
   and a Guest.
Limit number of guests and managed profiles that can
be added.

Added unit tests.

Bug: 15934700
Change-Id: I1a8f0fa38a91d71ef7b2980e05c974244dfc337a