SW-816: reused radb connections. Testing showed that opening/closing db connection too quickly in succession can lead to timeouts while waiting for sockets in TCP_WAIT state.

SW-816: implemented truncate trigger which cascades a truncate on resource_claim to resource_usage and resource_usage_delta

SW-816: improved speed of the RADBCommonTestMixin by only creating a postgres instance upon setUpClass, and applying a fresh radb schema every test via setUp

Resolve SW-815

See merge request !55

SW-816: bonus feature: refactored RADBCommonTest into a RADBCommonTestMixin which takes care of setting up a testing postgres radb instance, and which can be used in conjunction with a unittest.TestCase to do unittests on a fresh RADB instance. By using a mixin instead of chained inheritance we have better seperation of responsibility, and tools like pycharm can handle these tests better as well.

SW-816: modified radb insertSpecificationAndTask into insertOrUpdateSpecificationAndTask. This has the advantage that we do not have to reconnect predecessor relations, and in the webscheduler a re-insert of a task will now be visible as an update on an existing task, instead of a delete (disappear) followed by an insert (reappear). Catch task_predecessor_unique PostgresDBQueryExecutionError in the Specification class of the resourceassigner, so scheduling can continue even on tasks which were already known and already had links to predecessors.

SW-816: added test test_do_assignment_does_not_raise_on_inserting_predecessors which reproduces the bug of SW-816. It fails with a 'duplicate key value violates unique constraint task_predecessor_unique' error from the RABD when scheduling a successor task for the second time.

SW-816: rewrote t_resourceassigner to use a testing-RADB, thereby removing many wrong assumptions made in the mocks. The resource_assgner and its schedulers can still be simplified significantly if we just use the RADB as designed; just insert the claims, and let the RADB check/set the conlict status.

ROHD-2065: fixed typos

See merge request !56

Resolve SW-811

See merge request !51

SW-811: ToBus.send now retries to reconnect and resend the message upon connection loss. Added test for that as well.

SW-811: added test to prove that sending a message on a broken connection fails with a MessagingError

SW-810: renamed unused-IS614* to LV614*

See merge request !49