Restarts from restore-file does not work if restart occurs before a new checkpoint is written

Created by: suchenzang

Right now, if we were to launch a job with --restore-file and experience a job restart shortly thereafter (before a new checkpoint is written), we fail to resume again from the --restore-file and instead start from scratch again.

This should be fixed to restart from --restore-file (though if new checkpoints are present, should still continue to restart from latest and not the restore file).