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

docs/advanced/worker-pools.md

@@ -150,19 +150,15 @@ Create a cluster following the Google Cloud [tutorial](../cl/google-cloud.md#clu
 module "yavin-worker-pool" {
   source = "git::https://github.com/poseidon/typhoon//google-cloud/container-linux/kubernetes/workers?ref=v1.14.3"
 
-  providers = {
-    google = "google.default"
-  }
-
   # Google Cloud
   region       = "europe-west2"
-  network      = "${module.google-cloud-yavin.network_name}"
+  network      = module.google-cloud-yavin.network_name
   cluster_name = "yavin"
 
   # configuration
   name               = "yavin-16x"
-  kubeconfig         = "${module.google-cloud-yavin.kubeconfig}"
-  ssh_authorized_key = "${var.ssh_authorized_key}"
+  kubeconfig         = module.google-cloud-yavin.kubeconfig
+  ssh_authorized_key = var.ssh_authorized_key
   
   # optional
   worker_count = 2
@@ -200,9 +196,9 @@ The Google Cloud internal `workers` module supports a number of [variables](http
 |:-----|:------------|:--------|
 | name | Unique name (distinct from cluster name) | "yavin-16x" |
 | region | Region for the worker pool instances. May differ from the cluster's region | "europe-west2" |
-| network | Must be set to `network_name` output by cluster | "${module.cluster.network_name}" |
+| network | Must be set to `network_name` output by cluster | module.cluster.network_name |
 | cluster_name | Must be set to `cluster_name` of cluster | "yavin" |
-| kubeconfig | Must be set to `kubeconfig` output by cluster | "${module.cluster.kubeconfig}" |
+| kubeconfig | Must be set to `kubeconfig` output by cluster | module.cluster.kubeconfig |
 | ssh_authorized_key | SSH public key for user 'core' | "ssh-rsa AAAAB3NZ..." |
 
 Check the list of regions [docs](https://cloud.google.com/compute/docs/regions-zones/regions-zones) or with `gcloud compute regions list`.

docs/cl/google-cloud.md

@@ -10,15 +10,15 @@ Controllers are provisioned to run an `etcd-member` peer and a `kubelet` service
 
 * Google Cloud Account and Service Account
 * Google Cloud DNS Zone (registered Domain Name or delegated subdomain)
-* Terraform v0.11.x and [terraform-provider-ct](https://github.com/poseidon/terraform-provider-ct) installed locally
+* Terraform v0.12.x and [terraform-provider-ct](https://github.com/poseidon/terraform-provider-ct) installed locally
 
 ## Terraform Setup
 
-Install [Terraform](https://www.terraform.io/downloads.html) v0.11.x on your system.
+Install [Terraform](https://www.terraform.io/downloads.html) v0.12.x on your system.
 
 ```sh
 $ terraform version
-Terraform v0.11.14
+Terraform v0.12.0
 ```
 
 Add the [terraform-provider-ct](https://github.com/poseidon/terraform-provider-ct) plugin binary for your system to `~/.terraform.d/plugins/`, noting the final name.
@@ -49,37 +49,15 @@ Configure the Google Cloud provider to use your service account key, project-id,
 
 ```tf
 provider "google" {
-  version = "~> 2.7.0"
-  alias   = "default"
-
-  credentials = "${file("~/.config/google-cloud/terraform.json")}"
+  version     = "2.7.0"
   project     = "project-id"
   region      = "us-central1"
+  credentials = "${file("~/.config/google-cloud/terraform.json")}"
 }
 
 provider "ct" {
   version = "0.3.2"
 }
-
-provider "local" {
-  version = "~> 1.0"
-  alias = "default"
-}
-
-provider "null" {
-  version = "~> 1.0"
-  alias = "default"
-}
-
-provider "template" {
-  version = "~> 1.0"
-  alias = "default"
-}
-
-provider "tls" {
-  version = "~> 1.0"
-  alias = "default"
-}
 ```
 
 Additional configuration options are described in the `google` provider [docs](https://www.terraform.io/docs/providers/google/index.html).
@@ -93,15 +71,7 @@ Define a Kubernetes cluster using the module `google-cloud/container-linux/kuber
 
 ```tf
 module "google-cloud-yavin" {
-  source = "git::https://github.com/poseidon/typhoon//google-cloud/container-linux/kubernetes?ref=v1.14.3"
-  
-  providers = {
-    google   = "google.default"
-    local    = "local.default"
-    null     = "null.default"
-    template = "template.default"
-    tls      = "tls.default"
-  }
+  source = "git::https://github.com/poseidon/typhoon//google-cloud/container-linux/kubernetes?ref=v1.14.4"
 
   # Google Cloud
   cluster_name  = "yavin"

docs/index.md

@@ -49,15 +49,7 @@ Define a Kubernetes cluster by using the Terraform module for your chosen platfo
 
 ```tf
 module "google-cloud-yavin" {
-  source = "git::https://github.com/poseidon/typhoon//google-cloud/container-linux/kubernetes?ref=v1.14.3"
-  
-  providers = {
-    google   = "google.default"
-    local    = "local.default"
-    null     = "null.default"
-    template = "template.default"
-    tls      = "tls.default"
-  }
+  source = "git::https://github.com/poseidon/typhoon//google-cloud/container-linux/kubernetes?ref=v1.14.4"
 
   # Google Cloud
   cluster_name  = "yavin"