graph+autopilot: let autopilot use new graph ForEachNode method

Which passes a NodeRTx to the call-back instead of a `kvdb.RTx`.

graph/db/graph_cache_test.go

@@ -121,7 +121,7 @@ func TestGraphCacheAddNode(t *testing.T) {
 		assertCachedPolicyEqual(t, outPolicy1, toChannels[0].InPolicy)
 
 		// Now that we've inserted two nodes into the graph, check that
-		// we'll recover the same set of channels during ForEachNode.
+		// we'll recover the same set of channels during forEachNode.
 		nodes := make(map[route.Vertex]struct{})
 		chans := make(map[uint64]struct{})
 		_ = cache.ForEachNode(func(node route.Vertex,