lib/drmtest: Check that helper processes have died correctly

If the test gets stopped sometimes a helper process falls over.
We need to report this. Since we currently don't track helper
process to precisely we can't shut up the 2nd test failure messge.
This shouldn't happen anyway.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

lib/drmtest.c

@@ -1085,6 +1085,7 @@ void igt_stop_helper(struct igt_helper_process *proc)
 	while (waitpid(proc->pid, &status, 0) == -1 &&
 	       errno == -EINTR)
 		;
+	igt_assert(WIFSIGNALED(status) && WTERMSIG(status) == SIGQUIT);
 
 	proc->running = false;