Uncaught exception in QTestDatabaseHandler#afterTest causes unrelated test failures

When for some reason we fail to cleanup a database after running a test using the qt:database option an exception is raised and propagates up the stack. Not catching it in QTestDatabaseHandler#afterTest disrupts subsequent cleanup actions, which are not executed, and leads to failures in subsequent tests which are not related.

Moreover, the exception leaves QTestDatabaseHandler in an invalid state since the internal map holding the running databases is not updated.