request #7572 Backup of gitolite repositories doesn't manage 'in path' directory

Remove usage of system as it doesn't manage returned values properly

Change-Id: I838685644a771c8ee714dd5a985551081c1f95e5
Merge commit 'refs/changes/61/3161/4' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  request #7572 Backup of gitolite repositories doesn't manage 'in path' directory
This is Tuleap 7.6.99.57

Change-Id: I5fef28d197e8fb4c32ce9d5e773194264e98b479