Release the lock.

def release(self):
        """
        Release the lock.
        """
        query = 'DELETE FROM {cf} WHERE "lockId"=:lockId AND "claimId"=:claimId;'
        d = self._client.execute(query.format(cf=self._lock_table),
                                 {'lockId': self._lock_id, 'claimId': self._claim_id},
                                 ConsistencyLevel.QUORUM)

        def _log_release_time(result):
            if self._log and self._lock_acquired_seconds is not None:
                seconds = self._reactor.seconds() - self._lock_acquired_seconds
                self._log.msg('Released lock. Was held for {0} seconds'.format(seconds),
                              lock_held_time=seconds, result=result, **self._log_kwargs)
            return result

        return d.addBoth(_log_release_time)