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.
The nobody user/group may not synthesized by systemd.
To run tests the functionalities in such situation, this adds tests
by user/group by daemon, as it is expected to exists all environments.