MINOR: systemd wrapper: propagate exit status

Use HAProxy's exit status as the systemd wrapper's exit status instead
of always returning EXIT_SUCCESS, permitting the use of systemd's
`Restart = on-failure' logic.

src/haproxy-systemd-wrapper.c

@@ -184,5 +184,5 @@ int main(int argc, char **argv)
 
 	fprintf(stderr, SD_NOTICE "haproxy-systemd-wrapper: exit, haproxy RC=%d\n",
 			status);
-	return EXIT_SUCCESS;
+	return status;
 }