This allows the user to build any non-master branches of the related
repositories, which is helpful for local testing before pushing changes
to git.
Change-Id: I0c3349e9a60015472c96bd24fbf29aad57501a00
Let's use the "ADD" trick that we use for git repositories also for
the osmocom:nightly debian package feed. This way any change to the
package feed will result in a rebuild of the container.