request #6599: Have more meaningfull gerrit error messages

Change-Id: If5b1fbed0af6e71c4408c87ee6f94f2e8475b036
Merge commit 'refs/changes/26/2226/3' of http://gerrit.tuleap.net/tuleap into HEAD

* http://gerrit.tuleap.net/tuleap:
  request #6599: Have more meaningfull gerrit error messages

Change-Id: I13ba0f6d4f3ae17a1f5f2157a61155b251858526
This is Tuleap 6.11.99.50

Change-Id: I17716cf3867da2cd4fb57c6abc97d0bcc2c9dd3b