Implement networks routed through wesher

This adds an option for specifying a routed network. Every node route
that belongs to that routed network will be announced to the cluster and
every other node will direct traffic to that node for said route.

common/node.go

@@ -11,6 +11,7 @@ import (
 // nodeMeta holds metadata sent over the cluster
 type nodeMeta struct {
 	OverlayAddr net.IPNet
+	Routes      []net.IPNet
 	PubKey      string
 }