If sh is not bash, some builtin command behave slightly differently.
E.g. if sh is provided by busybox, its builtin test command does not check if
the path is a mount point or not, and 'test -w' only checks the access mode of
the inode. So, even if a readonly filesystem is mounted on a directory,
the test command may succeed.
To avoid such confusion, let's unconditionally use bash.
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.
In my understanding user group "3" (aka "sys") is kept for historical reasons
but not really useful these days. That's probably explained why this group
isn't defined on openSUSE.
Hence let's drop reference to this user group, this shouldn't lessen the
revelance of the test since SupplementaryGroups= is still tested with 2 other
groups.
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.
