Remove testtools.main() call from tests

There is no testtools.main() at all (this was a
unittest.main() before). Let's remove this unused
and non-working code.

The following code can be used if someone needs
to start tests manually:

    python -m unittest <test_file.py>

Change-Id: Id5162ac73825584df6c23dbe68786ff3355fc6ae
Merge "Remove testtools.main() call from tests"