Tries to lock and run cron jobs.

    Args:
      token: security token
      force: If True, force a run
      names: List of job names to run.  If unset, run them all

def RunOnce(self, token=None, force=False, names=None):
    """Tries to lock and run cron jobs.

    Args:
      token: security token
      force: If True, force a run
      names: List of job names to run.  If unset, run them all
    """
    names = names or self.ListJobs(token=token)
    urns = [self.CRON_JOBS_PATH.Add(name) for name in names]

    for cron_job_urn in urns:
      try:
        with aff4.FACTORY.OpenWithLock(
            cron_job_urn, blocking=False, token=token,
            lease_time=600) as cron_job:
          try:
            logging.info("Running cron job: %s", cron_job.urn)
            cron_job.Run(force=force)
          except Exception as e:  # pylint: disable=broad-except
            logging.exception("Error processing cron job %s: %s", cron_job.urn,
                              e)
            stats_collector_instance.Get().IncrementCounter(
                "cron_internal_error")

      except aff4.LockError:
        pass