Use run-tests.sh for tox coverage tests

The coverage tests mustn't run in parallel and must have a working
mongod instance like other tests.

So just use the run-tests.sh with a special flags --coverage

Fix bug #1199411

Change-Id: Id750697a69213ee753280b7adc8f726dbdb1fca5
Merge "Use run-tests.sh for tox coverage tests"