ignore sigchld when shutting down the supervised process

We need to do this to skip the zombie state for the child process since
we are not easily able to wait() for it.

src/rc/supervise-daemon.c

@@ -753,6 +753,7 @@ int main(int argc, char **argv)
 		while (!exiting) {
 			wait(&i);
 			if (exiting) {
+				signal_setup(SIGCHLD, SIG_IGN);
 				syslog(LOG_INFO, "stopping %s, pid %d", exec, child_pid);
 				nkilled = run_stop_schedule(applet, exec, NULL, child_pid,
 						0, false, false, true);