Turns out we can, apart from just building the module, "shove" it into
the SELinux database in a chroot as well. This brings quite significant
time savings, as the SELinux db rebuild takes 2 - 5 minutes in a VM
without acceleration (and takes currently ~half of the runtime of the test
in the C8S job).
Those are all consumed by our parser, so they all support comments.
I was considering whether they should have a license header at all,
but in the end I decided to add it because those files are often created
by copying parts of real unit files. And if the real ones have a license,
then those might as well. It's easier to add it than to make an exception.