stop.sh doesn't work after two starts

[rmader]

When running start.sh two times in a row, the second start righly aborts (although not stated in output)
But when I then run stop.sh, I can't stop the running instance anymore and have to kill it via taskmanager.

Steps to reproduce:

• run start.sh two times
• run stop.sh two times
• check if there's still a runnig loklak instance in taskmanager

This lack of output and checking is sometimes really confusing and I think it happens many of us from time to time.

See #337

[rmader]

see above