Change flannel port from 8472 to 4789

* Change flannel port from the kernel default 8472 to the
IANA assigned VXLAN port 4789
* Update firewall rules or security groups for VXLAN
* Why now? Calico now offers its own VXLAN backend so
standardizing on the IANA port will simplify config
* https://github.com/coreos/flannel/blob/master/Documentation/backends.md#vxlan

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

@@ -1,6 +1,6 @@
 # Self-hosted Kubernetes assets (kubeconfig, manifests)
 module "bootkube" {
-  source = "git::https://github.com/poseidon/terraform-render-bootkube.git?ref=b96d641f6d42cf5d9bf3ac36f557aa21cc157680"
+  source = "git::https://github.com/poseidon/terraform-render-bootkube.git?ref=fc7a6fb20abe41ccd40f3449ee8ee7bba7bd9932"
 
   cluster_name          = "${var.cluster_name}"
   api_servers           = ["${format("%s.%s", var.cluster_name, var.dns_zone)}"]

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

@@ -78,16 +78,16 @@ resource "google_compute_firewall" "internal-bgp" {
   target_tags = ["${var.cluster_name}-controller", "${var.cluster_name}-worker"]
 }
 
-# flannel
-resource "google_compute_firewall" "internal-flannel" {
+# flannel VXLAN
+resource "google_compute_firewall" "internal-vxlan" {
   count = "${var.networking == "flannel" ? 1 : 0}"
 
-  name    = "${var.cluster_name}-internal-flannel"
+  name    = "${var.cluster_name}-internal-vxlan"
   network = "${google_compute_network.network.name}"
 
   allow {
     protocol = "udp"
-    ports    = [8472]
+    ports    = [4789]
   }
 
   source_tags = ["${var.cluster_name}-controller", "${var.cluster_name}-worker"]