Fix all jBPM 5 unit tests so that they work with a selection of real (not in-memory) databases

While the jbpm 5 unit tests that use persistence all succeed when using the H2 database, this is not true when the tests run on other databases.

This has various causes, depending on the test or the database:

• it can be because the test does not record the start situation
• it can also be because the transaction support in the test can also not be correct.
• lastly, it can/might also be because transaction support in jbpm 5 is not correct.