Fix org#2500 .bvfs_get_jobids jobid=X must return X in the list part2

Fix org#2500 .bvfs_get_jobids jobid=X must return X in the list part2

- restrict this feature to the ".bvfs_get_jobids" command only
- else any call with a jcr->JobId != 0 force the function to use it
  this is not what we want.
- notice the following change in the behaviour of the .bvfs_get_jobids
  command when a job has been migrated :
| JobId | Name             | StartTime           | Type | Level | JobFiles
+-------+------------------+---------------------+------+-------+---------
| 1     | MigrationJobSave | 2021-05-04 11:16:26 | M    | F     | 3131
| 5     | MigrationJobSave | 2021-05-04 11:16:26 | B    | F     | 3131
*.bvfs_get_jobids jobid=1
5 <== before the change
*.bvfs_get_jobids jobid=1
<EMPTY-LINE>  <== after the change