Rotate the files to disk.

        This is done by calling `store.close()` on each store, bumping the
        batchno and reopening the stores using their factories.

def rotate(self):
        """Rotate the files to disk.

        This is done by calling `store.close()` on each store, bumping the
        batchno and reopening the stores using their factories.

        """
        self._logger.info('Rotating data files. New batch number will be: %s',
                          self.batchno + 1)
        self.estore.close()
        self.estore = None
        self.batchno += 1
        self.estore = self._open_event_store()