We passes log level through kernel command line. It is not necessary to
set to debug level at the beginning, and set to info at the end.
This is important when a test has several subtests. If a subtest sets
log level to info at the end, then subsequent tests may not generate any
useful logs.
This also makes shebang always use env command, and drops unnecessary
'bash -c' or 'sh -c' when a signle command is invoked in the shell,
like sleep or echo.
This changes little in behaviour, the conceptual part is more important. The
non-Ex variant is the actual name on the command line, and we should use the
non-Ex D-Bus property too, if it works. This increases compatibility with old
versions. But the code was mostly doing the right thing. Even the tests tested
the right thing.
Follow-up for b3d593673c and
898fc00e79.
The test is simplified by taking advantage of the fact that both names
on the commandline are supposed to behave identically.
Partially resolves https://github.com/systemd/systemd/issues/37174.
Having these named differently than the test itself mostly creates
unecessary confusion and makes writing logic against the tests harder
so let's rename the testsuite-xx units and scripts to just use the
test name itself.