Fix for multi-repo tag chckouts

Zuul prepares the tag reference for the project which triggers the build,
but not other repos, so we have to fall back to the gerrit repo to find
the tag.

Quick fix needed to prepare 0.8.3 rc1 build.

Change-Id: Ibf1c97ab2a2d9146b873d5b4dc1f98fa993d0455