Allow to specify port, and remove session id.

So now the way to address a node is in the form of:
`ip10_0_1_9-9200.play-with-docker.com`

api.go

@@ -60,7 +60,8 @@ func main() {
 	r.Handle("/sessions/{sessionId}/ws/", server)
 
 	// Reverse proxy
-	r.Host(`{node}.{session}.play-with-docker.com`).Handler(handlers.NewMultipleHostReverseProxy())
+	r.Host(`{node}-{port:[0-9]*}.play-with-docker.com`).Handler(handlers.NewMultipleHostReverseProxy())
+	r.Host(`{node}.play-with-docker.com`).Handler(handlers.NewMultipleHostReverseProxy())
 
 	n := negroni.Classic()
 	n.UseHandler(r)