[SP-1062] Backport of PDI-10987 - Vectorwise bulk loader step parallel execution (5.0)

* Added: look PDI-10987 
```
 +        if ( vwLoadMonitorThread != null ) {
 +          vwLoadMonitorThread.join();
 +        }
 +        setOutputDone();
```
* also was indirectly back-ported PDI-6512 as it was needed for fix.