Make unit tests cleanup a DB after finish

Unit tests don't cleanup a DB after successful finish.
It is an issue if I use one DB for all kind of tests. Especially with hardcoded primary keys in fixtures.

This fix make tests do a housekeeping after them.
is tearDown always called? I am for making the  the change in general but maybe we want to keep the call in setUp() to be able to work even with a corrupted DB that may happen when phpunit crashes?