Migrate Google Cloud module Terraform v0.11 to v0.12

* Replace v0.11 bracket type hints with Terraform v0.12 list expressions
* Use expression syntax instead of interpolated strings, where suggested
* Update Google Cloud tutorial and worker pools documentation
* Define Terraform and plugin version requirements in versions.tf
  * Require google ~> 2.5 to support Terraform v0.12
  * Require ct ~> 0.3.2 to support Terraform v0.12

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

@@ -1,53 +1,53 @@
 variable "name" {
-  type        = "string"
+  type        = string
   description = "Unique name for the worker pool"
 }
 
 variable "cluster_name" {
-  type        = "string"
+  type        = string
   description = "Must be set to `cluster_name of cluster`"
 }
 
 # Google Cloud
 
 variable "region" {
-  type        = "string"
+  type        = string
   description = "Must be set to `region` of cluster"
 }
 
 variable "network" {
-  type        = "string"
+  type        = string
   description = "Must be set to `network_name` output by cluster"
 }
 
 # instances
 
 variable "worker_count" {
-  type        = "string"
+  type        = string
   default     = "1"
   description = "Number of worker compute instances the instance group should manage"
 }
 
 variable "machine_type" {
-  type        = "string"
+  type        = string
   default     = "n1-standard-1"
   description = "Machine type for compute instances (e.g. gcloud compute machine-types list)"
 }
 
 variable "os_image" {
-  type        = "string"
+  type        = string
   default     = "coreos-stable"
   description = "Container Linux image for compute instanges (e.g. gcloud compute images list)"
 }
 
 variable "disk_size" {
-  type        = "string"
+  type        = string
   default     = "40"
   description = "Size of the disk in GB"
 }
 
 variable "preemptible" {
-  type        = "string"
+  type        = string
   default     = "false"
   description = "If enabled, Compute Engine will terminate instances randomly within 24 hours"
 }
@@ -55,12 +55,12 @@ variable "preemptible" {
 # configuration
 
 variable "kubeconfig" {
-  type        = "string"
+  type        = string
   description = "Must be set to `kubeconfig` output by cluster"
 }
 
 variable "ssh_authorized_key" {
-  type        = "string"
+  type        = string
   description = "SSH public key for user 'core'"
 }
 
@@ -70,32 +70,34 @@ CIDR IPv4 range to assign Kubernetes services.
 The 1st IP will be reserved for kube_apiserver, the 10th IP will be reserved for coredns.
 EOD
 
-  type    = "string"
+
+  type = string
   default = "10.3.0.0/16"
 }
 
 variable "cluster_domain_suffix" {
   description = "Queries for domains with the suffix will be answered by coredns. Default is cluster.local (e.g. foo.default.svc.cluster.local) "
-  type        = "string"
-  default     = "cluster.local"
+  type = string
+  default = "cluster.local"
 }
 
 variable "clc_snippets" {
-  type        = "list"
+  type = list(string)
   description = "Container Linux Config snippets"
-  default     = []
+  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"
 }
+