Error reply to a command.

        Returns True so it is suitable as an `~MockupDB.autoresponds` handler.

def command_err(self, code=1, errmsg='MockupDB command failure',
                    *args, **kwargs):
        """Error reply to a command.

        Returns True so it is suitable as an `~MockupDB.autoresponds` handler.
        """
        kwargs.setdefault('ok', 0)
        kwargs['code'] = code
        kwargs['errmsg'] = errmsg
        self.replies(*args, **kwargs)
        return True