We want to retain *some* of the full paths in order to test more code paths.
But the default should be to use the command name only. This makes the tests
less visually cluttered.
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 man pages state that the '+' prefix in Exec* directives should
ignore filesystem namespacing options such as PrivateTmp. Now it does.
This is very similar to #8842, just with PrivateTmp instead of
PrivateDevices.