resources: Update state checks

The mgmt graph depends on state tracking to eliminate redundant pokes.
With the Watch loop now able to produce events quickly, it should no
longer play a part in determining the vertex state. This simplifies the
resource API as well!

resources/nspawn.go

@@ -140,7 +140,6 @@ func (obj *NspawnRes) Watch(processChan chan *event.Event) error {
 	var exit *error
 
 	for {
-		obj.SetState(ResStateWatching)
 		select {
 		case event := <-buschan:
 			// process org.freedesktop.machine1 events for this resource's name