test: fix tool option parsing tests for signals

Not sure how this ever worked correctly: a process terminated by a signal has
the negative signo as return code. This would apply to every debug-events and
debug-gui test because they have to get killed by a signal. This failed
occasionally, presumably a race with the GTK startup/signal handler/whatever.

Fix this by a) sending SIGQUIT because that won't get handled by the tools and
b) prending that if we get a -SIGQUIT exit code, everything is fine.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>