fix graceful_shutdown

(transplanted from a00ae0dd2b05ee9d19eecead2e95c7c07f16c560)

vispa/controller/root.py

@@ -278,6 +278,7 @@ class RootController(AbstractController):
         else:
             logger.warn(
                 "Graceful shutdown started")
+            _cb_graceful_shutdown(None, None)
             vispa.subscribe("bus.session_removed", _cb_graceful_shutdown)