When DynamicUser= is enabled, we need LD_PRELOAD to be configured
correctly as the tests will load systemd's nss module which will complain
when built with sanitizers if the sanitizer libraries were not loaded
first.
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.
Before this, tests are split into two categories, system and user, but
both are running in fully privileged environment. Hence, unprivileged
user scope was mostly not covered by the test.
Let's run all tests in both system and user scopes, and drop capabilities
when Manager is running in user scope.
This also makes the host environment protected more from the test run.
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.
