This could be shared more easily with e.g. rpm-ostree, but what I'm currently
working on is installed, privileged (potentially destructive, i.e. VM) tests
that will source this separately from the current `libtest.sh`. That does work
installed, but in practice is oriented around unit (uninstalled, unprivileged)
tests.
Closes: #807
Approved by: jlebon
Colin Walters