weston-launch: Don't exit on SIGTERM

Instead, forward signal to weston and wait for weston to clean up nicely.
Weston relies on weston-launch being around to shut down correctly,
so don't exit until we get the SIGCHLD from weston.  This make
killall weston-launch work properly.

https://bugs.freedesktop.org/show_bug.cgi?id=62910

src/weston-launch.c

@@ -453,13 +453,9 @@ handle_signal(struct weston_launch *wl)
 		}
 		break;
 	case SIGTERM:
-		if (wl->child)
-			kill(wl->child, SIGTERM);
-		quit(wl, 0);
-		break;
 	case SIGINT:
 		if (wl->child)
-			kill(wl->child, SIGTERM);
+			kill(wl->child, sig.ssi_signo);
 		break;
 	default:
 		return -1;