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

digital-ocean/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)}"]

digital-ocean/container-linux/kubernetes/network.tf

@@ -12,7 +12,7 @@ resource "digitalocean_firewall" "rules" {
     },
     {
       protocol    = "udp"
-      port_range  = "8472"
+      port_range  = "4789"
       source_tags = ["${digitalocean_tag.controllers.name}", "${digitalocean_tag.workers.name}"]
     },
     {