Reads all cron job runs for a given job id.

def ReadCronJobRuns(self, job_id):
    """Reads all cron job runs for a given job id."""
    runs = [
        run for run in itervalues(self.cronjob_runs)
        if run.cron_job_id == job_id
    ]
    return sorted(runs, key=lambda run: run.started_at, reverse=True)