def cleanup(self, keep=5):
        """Remove all but the ``keep`` most recent releases.

        If any of the candidates for deletion are pointed to by the
        'current' symlink, they will not be deleted.

        This method performs N + 2 network operations where N is the
        number of old releases that are cleaned up.

        :param int keep: Number of old releases to keep around
        """
        releases = self.get_releases()
        current_version = self.get_current_release()
        to_delete = [version for version in releases[keep:] if version != current_version]

        for release in to_delete:
            self._runner.run("rm -rf '{0}'".format(os.path.join(self._releases, release)))