Log when connection is closed, if needed call callback.

def connection_lost(self, exc):
        """Log when connection is closed, if needed call callback."""
        if exc:
            self.logger.error('disconnected due to error')
        else:
            self.logger.info('disconnected because of close/abort.')
        if self.disconnect_callback:
            asyncio.ensure_future(self.disconnect_callback(), loop=self.loop)