Fix deletion of HBAC Rules when there are SELinux user maps defined
    
    When deleting an HBAC rule we need to ensure that an SELinux user
    map isn't pointing at it. We need to take what is the cn of the HBAC
    rule and see if that rule exists, then return the dn to that rule.
    
    The search was not being done properly and wasn't enforcing uniqueness.
    It could have returned partial matches as well (so tests for the
    search test).
    
    https://fedorahosted.org/freeipa/ticket/2269