Suppress missing cn=schema compat on installation
    
    The schema compat plugin is disabled on upgrades but it is
    possible that it is not configured at all and this will
    produce a rather nasty looking error message.
    
    Check to see if it is configured at all before trying to
    disable it.
    
    https://pagure.io/freeipa/issue/6610
    
    Reviewed-By: Christian Heimes <cheimes@redhat.com>