Fix direct execution of AppImages

Fetch a list of all child PIDs before forwarding the termination signal.
Once the main process is terminated, forward that term signal to all found children also (if they are still running)

overlay/usr/bin/sunshine-stop

@@ -36,6 +36,7 @@ echo "  - Found initial sunshine-run PID '${process_pid}'."
 # Send a INT signal to the PID
 echo "  - Sending SIGINT to PID '${process_pid}'."
 kill -INT "${process_pid}" || true
+sleep 1
 
 # Run a loop to check for any other "sunshine-run" processes and send them also a INT signal
 echo "  - Checking for other sunshine-run processes..."