Test procedure for ingesting tarballs with package updates

[bedroge]

If we need to patch some package (e.g. Python/glibc) in our compatibility (or software) layer, we need to figure out how to catch the changes on a build node and do the actual change on a publisher node. Modifying and adding files is simple, but the tricky part is removing files.

Ultimately, we can perhaps tar the entire new compatibility layer directory, and ingest that with the -d option to remove the old directory. We need to think about this and test what does (not) work.

[bedroge]

Asked this on the CVMFS Mattermost: at the moment you can't use a single ingest command to remove and re-add the same directory, it may be supported in the future. You can run two subsequent ingest commands, but in theory it could happen that clients then don't see this directory for a while (if the Stratum 1 does a snapshot in the meantime). So for now we can start a manual transaction, wipe the old folder, extract the new tarball, and publish the changes.