Return different code when stopping and already stopped

Both the factory and frontend stop procedure now return:
- 0 if stop was successfull
- 1 if invoked incorrectly or unable to stop the services (some unkillable process)
- 2 if it was already stopped

Exit code 1 will block composite actions like restart, reconfig, ...
Exit code 2 is OK (will continue to the next steps), like 0.