request #7327 Tv3 export to Tv5: cannot migrate trackers not readable by anonymous

* A system event was calling code that didn't throw exception so it was not
  visible that errors were present
* Even if it did, at the end of the process, the TRACKER_V3_MIGRATION was
  always marked as done even with errors
* Finally, user was not explicitly given to conversion methods so it was
  actually done by 0, anonymous

Change-Id: I70cec0834717edcac698cdacd7d5db9eb8524823
Merge commit 'refs/changes/66/2866/2' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  request #7327 Tv3 export to Tv5: cannot migrate trackers not readable by anonymous

Change-Id: Ib06e9d1881565cc59920295e61bcb0b918a2ddd3
This is Tuleap 7.3.99.55

Change-Id: I0fb111e1bf68e5792deac37a21e8671995aad65a