Add Container Linux Config snippets feature

* Introduce the ability to support Container Linux Config
"snippets" for controllers and workers on cloud platforms.
This allows end-users to customize hosts by providing Container
Linux configs that are additively merged into the base configs
defined by Typhoon. Config snippets are validated, merged, and
show any errors during `terraform plan`
* Example uses include adding systemd units, network configs,
mounts, files, raid arrays, or other disk provisioning features
provided by Container Linux Configs (using Ignition low-level)
* Requires terraform-provider-ct v0.2.1 plugin

google-cloud/container-linux/kubernetes/workers/variables.tf

@@ -59,7 +59,7 @@ variable "kubeconfig" {
 
 variable "ssh_authorized_key" {
   type        = "string"
-  description = "SSH public key for logging in as user 'core'"
+  description = "SSH public key for user 'core'"
 }
 
 variable "service_cidr" {
@@ -78,16 +78,22 @@ variable "cluster_domain_suffix" {
   default     = "cluster.local"
 }
 
+variable "clc_snippets" {
+  type        = "list"
+  description = "Container Linux Config snippets"
+  default     = []
+}
+
 # unofficial, undocumented, unsupported, temporary
 
 variable "accelerator_type" {
-  type = "string"
-  default = ""
+  type        = "string"
+  default     = ""
   description = "Google Compute Engine accelerator type (e.g. nvidia-tesla-k80, see gcloud compute accelerator-types list)"
 }
 
 variable "accelerator_count" {
-  type = "string"
-  default = "0"
+  type        = "string"
+  default     = "0"
   description = "Number of compute engine accelerators"
 }

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

@@ -32,6 +32,7 @@ data "template_file" "worker_config" {
 data "ct_config" "worker_ign" {
   content      = "${data.template_file.worker_config.rendered}"
   pretty_print = false
+  snippets     = ["${var.clc_snippets}"]
 }
 
 resource "google_compute_instance_template" "worker" {
@@ -63,11 +64,11 @@ resource "google_compute_instance_template" "worker" {
   }
 
   can_ip_forward = true
-  tags = ["worker", "${var.cluster_name}-worker", "${var.name}-worker"]
+  tags           = ["worker", "${var.cluster_name}-worker", "${var.name}-worker"]
 
   guest_accelerator {
     count = "${var.accelerator_count}"
-    type = "${var.accelerator_type}"
+    type  = "${var.accelerator_type}"
   }
 
   lifecycle {