*config-show: Do not show empty roles/attributes
    
    If the role or attribute is empty (i.e. no server provides the role or
    the caller has no read access to  the required information) do not
    return empty attributes. This is consistent with other behavior
    displayed by optional multivalued Params.
    
    https://pagure.io/freeipa/issue/7029
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>