test: Rework TEST-02-UNITTESTS

test: Rework TEST-02-UNITTESTS

Currently, A large amount of unit test output is logged directly
to the console instead of to the per test log file as any subprocesses
executed by a test manager will detect that stderr is not connected
to the journal and log directly to /dev/console instead.

To solve this issue, let's make sure all tests are connected directly
to the journal by running them with systemd-run. We also simplify the
entire test script by getting rid of the custom queue and replicating
it with xargs instead. By using bash's function export feature, we can
make our run_test() function available to the bash subprocess spawned
by xargs.

Once a test is finished, we read its logs from the journal and put them
in the appropriate file if needed.