Make sure selinuxusemap behaves consistently to HBAC rule
    
    Both selinuxusermap-add and selinuxusermap-mod commands now behave
    consistently in not allowing user/host category or user/host members
    and HBAC rule being set at the same time. Also adds a bunch of unit
    tests that check this behaviour.
    
    https://fedorahosted.org/freeipa/ticket/2983