Identical branch HEADs can result in Vagrant building from the wrong branch

It’s expected that Vagrant’s rake build starts a build from the checked out branch. However, if the current commit doesn’t have a unique symbolic reference there’s no guarantee the expected branch is built. For instance, for branches that just update the corresponding APT suite (and hence have empty deltas against devel) Vagrant may decide to build from devel instead, so the updates in the APT suite are not used.

The reason is the way we try to restore the branch name from the current commit using git symbolic-ref in build-tals. We should instead explicitly pass the checked out branch name or tag (and perhaps provide a TAILS_BUILD_OPTION called branch=<branch-or-tag-name> to allow specifying it explicitly) that then is passed to build-tail in our Rakefile.

Original created by @anonym on 7182 (Redmine)