run-tests: define cleanup() on unittest class
We need a cleanup() on our unittest TestCase class to conform with the
execution API. This will eventually be replaced by tearDown().
run-tests: teach Test instances whether they are in unittest mode
Tests executing in unittest mode behave a little differently. For
example, they report their results to a TestResult rather than just
printing. This patch paves the way for better integration of Test into
the unittest framework.