Shut down kubernetes watcher(s) gracefully
The code inside the for-loop of the watcher stream is only executed when a kubernetes event happens. Therefore, a threading 'stop' event as in publish_status_periodically (component.py) would only be checked for after an incoming kubernetes event. This means that the watcher thread does not get stopped properly when villas-controller is shut down.
- check for threading event inside watch stream loop
- on shutdown, trigger kubernetes event and stop the watcher (w.stop())