pgraph, resources: Clean up the event system around the resources

This cleans up some of the resource events and also reorganizes the
struct for simplicity. This should hopefully kill off at least one race
which would cause unnecessary blocking!

Yes this patch is a bit yucky, but so was the bug I was fighting with!

pgraph/actions.go

@@ -677,6 +677,7 @@ func (g *Graph) Exit() {
 		// XXX: we can do this to quiesce, but it's not necessary now
 
 		v.SendEvent(event.EventExit, nil)
+		v.Res.WaitGroup().Wait()
 	}
 	g.wg.Wait() // for now, this doesn't need to be a separate Wait() method
 }

pgraph/pgraph.go

@@ -588,6 +588,7 @@ func (g *Graph) GraphSync(oldGraph *Graph) (*Graph, error) {
 		if !VertexContains(v, vertexKeep) {
 			// wait for exit before starting new graph!
 			v.SendEvent(event.EventExit, nil) // sync
+			v.Res.WaitGroup().Wait()
 			oldGraph.DeleteVertex(v)
 		}
 	}