ipa-adtrust-install does not re-add member in adtrust agents group
    
    When a CIFS service exists and adtrust agents group does not
    have it as a member attribute (for whatever reason), re-running
    ipa-adtrust-install does not fix the inconsistency.
    
    Make the installer more robust by being able to fix the inconsistency.
    
    https://fedorahosted.org/freeipa/ticket/4464
    
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>