Rollback on SSH driver uses _save_ssh() which doesn't exist

[ktbyers]

    def _rollback_ssh(self, backup_file):
        command = 'rollback running-config file %s' % backup_file
        result = self.device.send_command(command)
        if 'completed' not in result.lower():
            raise ReplaceConfigException(result)
        self._save_ssh()

That _save_ssh() method doesn't exit.