exiting start script causes processes to be terminated

[kilrau]

When exiting the script e.g. in

waiting for BTC channel to be active
.................................^C

All processes get killed (check ps aux). Exiting the script should never kill any processes like lnd, ltcd, raiden or xud. Only xud-simnet-stop should.

[kilrau]

Should be an easy fix. Feel free to take over if you have some capa @michael1011