... when a RunWorker reportStopped(). We have now always a
"main" RunWorker (again) that is in a better position to decide
what to do with "lower" worker states than the RunControl.

The overall RunControl stopped state meaning is not changed:
It is Stopped if all workers are Stopped (or Done, or Failed)

Change-Id: I04ce6a8cb5b2067ec05fd506f6adc6ca65de0c39
Reviewed-by: Christian Stenger <christian.stenger@qt.io>