task.py: Get updated database version
This commit fixes the issue of having STOPPED jobs stuck in that state. I have assumptions on why the commit fixes the issue but no certainty. When entering the `schedule_run` controller, web2py loads the database in its current state. If someone then clicks on to run the sample that is currently being preprocessed, the task will be put in STOPPED state to wait for the preprocess to finish. Once the preprocess is finished, we query the DB to know which tasks have been stopped. But as the DB has been loaded at the start of the controller, it is not up-to-date anymore and doesn't get all the STOPPED jobs. Doing a db.commit() just before querying the STOPPED jobs could refresh the loaded DB. Fix #2053.