Improve gitlab-ci support regarding git-bundle

[zagy]

In gitlabci the local repo is in a detached head state (for some reason I do not comprehend).

When deploying batou fails to create the bundle because <remoterev>..<branch> doesn't work, because there is no branch locally. Running git branch -f $CI_COMMIT_BRANCH origin/$CI_COMMIT_BRANCH fixes this, but that seems unnecessary.

When creating the bundle we could try <remoterev>..<localrev> where localrev is probably what git rev-parse head puts out.