allow for more flexibility when requesting service keytab
    
    The service installers can now override the methods for cleaning up
    stale keytabs and changing file ownership of the newly acquired keytabs.
    
    The default actions should be usable by most installers without specific
    overriding.
    
    https://fedorahosted.org/freeipa/ticket/6638
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>