Log disconnects.

def close(self):
        """
        Log disconnects.

        """
        time_spent = time.time() - self.time_start
        logger.debug(
            '<{}> Disconnect from [{}]:{}, time spent {:.3f} seconds'.format(
                self.id, self.client_ip, self.client_port, time_spent))
        return Milter.CONTINUE