Reads a cronjob from the database.

def ReadCronJobs(self, cronjob_ids=None):
    """Reads a cronjob from the database."""
    if cronjob_ids is None:
      res = [job.Copy() for job in itervalues(self.cronjobs)]

    else:
      res = []
      for job_id in cronjob_ids:
        try:
          res.append(self.cronjobs[job_id].Copy())
        except KeyError:
          raise db.UnknownCronJobError("Cron job with id %s not found." %
                                       job_id)

    for job in res:
      lease = self.cronjob_leases.get(job.cron_job_id)
      if lease:
        job.leased_until, job.leased_by = lease
    return res