Print membership for #by_group and #by_user.

def parse_membership(header_string, membership):  # pragma: no cover
        """Print membership for #by_group and #by_user."""
        print(header_string, "\n{}".format('=' * len(header_string)))
        for key, values in membership.items():
            if values is None:
                continue
            print('- ', key)
            for value in values:
                print("\t- {}".format(value))