private void updateFinishTimeInfo(FinishTimeInfo finishTimeInfo, BackfillInfo info, long jobFinishTime) {
      updateLastBackfillTsSaved(finishTimeInfo, info);
      // Update max finish time, if required.
      if (finishTimeInfo._maxFinishTime < jobFinishTime) {
        finishTimeInfo._maxFinishTime = jobFinishTime;
      }
    }
Get applicable finish time used while storing in app finish times map. This would typically be the app finish
time for apps fetched from RM. But for backfill jobs, if finish time could not be determined at the time of
fetching jobs for backfill, we will use the backfill ts fetched from backfill_info table instead (0 will be used
if an entry in backfill_info table could not be found as well).

@return applicable finish time.
app/com/linkedin/drelephant/ElephantRunner.java