digital-ocean: Join name.dns_zone for controller domain

* Output the DNS FQDNs, IPv4 addresses, and IPv6 addresses

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

@@ -3,7 +3,7 @@ module "bootkube" {
   source = "git::https://github.com/dghubble/bootkube-terraform.git?ref=v0.6.0"
 
   cluster_name                  = "${var.cluster_name}"
-  api_servers                   = ["${var.k8s_domain_name}"]
+  api_servers                   = ["${format("%s.%s", var.cluster_name, var.dns_zone)}"]
   etcd_servers                  = ["http://127.0.0.1:2379"]
   asset_dir                     = "${var.asset_dir}"
   pod_cidr                      = "${var.pod_cidr}"

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

@@ -1,9 +1,9 @@
 output "controllers_dns" {
-  value = "${digitalocean_record.controllers.fqdn}"
+  value = "${digitalocean_record.controllers.0.fqdn}"
 }
 
 output "workers_dns" {
-  value = "${digitalocean_record.workers.fqdn}"
+  value = "${digitalocean_record.workers.0.fqdn}"
 }
 
 output "controllers_ipv4" {

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

@@ -49,11 +49,6 @@ variable "ssh_fingerprints" {
 
 # bootkube assets
 
-variable "k8s_domain_name" {
-  type        = "string"
-  description = "Controller DNS name which resolves to the controller instance. Kubectl and workers use TLS client credentials to communicate via this endpoint."
-}
-
 variable "asset_dir" {
   description = "Path to a directory where generated assets should be placed (contains secrets)"
   type        = "string"