gdbus-connection-loss: Fix leak in test

https://bugzilla.gnome.org/show_bug.cgi?id=711802

gio/tests/gdbus-connection-loss.c

@@ -139,7 +139,10 @@ main (int   argc,
 
   ret = g_test_run();
 
+  session_bus_down ();
+
   g_object_unref (c);
+  g_main_loop_unref (loop);
 
   return ret;
 }