[LMS-2328] reopened + refixed

[LMS-2389] error handling improvements
1) Do not propagate exceptions from AbstractOmnscientTopLevelDataSetRegistrator to DirectoryWatcher - errors are dealt within the class itself when transactions are rolled back
2) Allow DssUploadClient to see exceptions that are not happening inside a transaction boundary (e.g. Jython scripts fails before it creates a transaction).

SVN: 22057