Allow broadcast ip addresses
    
    Currently environments may use prefix /31 on point-to-point connections what
    makes IPA validators to fail. IPA should not care if IP address is broadcast
    or not. In some cases (when prefix is not specified) IPA cannot decide
    properly if broadcast address is really broadcast.
    
    This commit allows usage of broadcast addresses in:
    * host plugin
    * dns plugin
    * server-installer
    * client-installer
    
    https://fedorahosted.org/freeipa/ticket/5814
    
    Reviewed-By: David Kupka <dkupka@redhat.com>