Rollback release tag on Drive-package job failure

As we saw with the 2.5.4 beta release, the related Drive-package job failed (https://qa.nuxeo.org/jenkins/view/Drive/job/Drive/job/Drive-beta/45/).

The process is:

• create the release tag
• call the Drive-package job (it needes the release tag, that's why we seted up below)
• update the release notes on GitHub

On any failure, the release tag must be removed.