This seems to be the cleanest and simplest way of properly terminating
kas while one or more sub-processes are running: just ignore the signal.
The sub-processes will get it as well, and they will terminate
themselves properly. kas will get an error then and shut down. Problem
solved.
Forwarding the signal didn't work reliably anyway because we couldn't
count on kas being a process group leader in all cases.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>