i have improved the job executor test

3 scenarios are now tested:

testSuccessfulMessageProcessing sends a configurable number of TestMessage's to the job executor. the execution of the test message will add the message id to the list and that is then verified. by default there are 5 messages to process and a 10 seconds timeout

testMessagesPresentUponJobExecutorStartUp does the same, but this time the messages are inserted before the job executor starts.

testFailedMessageProcessing now shows that also a failed message will end up in the PvmDbSession.findDeadJobs() (aka DLQ) this one pointed out that a lot of things were missing in the failure scenario :-)