Fix firewall to allow etcd client traffic between controllers

* Broaden internal-etcd firewall rule to allow etcd client
traffic (2379) from other controller nodes
* Previously, kube-apiservers were only able to connect to their
node's local etcd peer. While master node outages were tolerated,
reaching a healthy peer took longer than neccessary in some cases
* Reduce time needed to bootstrap a cluster

google-cloud/container-linux/kubernetes/network.tf

@@ -23,7 +23,7 @@ resource "google_compute_firewall" "internal-etcd" {
 
   allow {
     protocol = "tcp"
-    ports    = [2380]
+    ports    = [2379, 2380]
   }
 
   source_tags = ["${var.cluster_name}-controller"]