region is required for google_compute_subnetwork

[sunggun-yu]

My environment is on GKE with shared VPC network.
And, I've got an error below when I tried 'terraform plan'. I believe this PR fix my issue.

data.google_compute_subnetwork.gke_subnetwork: Cannot determine region: set in this resource, or set provider-level 'region' or 'zone'.

Terraform Code:

module "gke-cluster-my-cluster" {
  source              = "github.com/terraform-google-modules/terraform-google-kubernetes-engine"
  project_id          = "my_project"
  name                = "my_cluster"
  kubernetes_version  = "1.10.6-gke.2"
  regional            = false
  region              = "us-east4"
  zones               = ["us-east4-a"]
  network_project_id  = "my_network_project"
  network             = "my_network"
  subnetwork          = "my_subnet"
  ip_range_pods       = "my_cidr_container"
  ip_range_services   = "my_cidr_service"
  network_policy      = true
  http_load_balancing = true

  node_pools = [
    {
      name                     = "my_node_pool"
      image_type               = "COS"
      instance_service_account = "my_service_account@my_project.iam.gserviceaccount.com"
      machine_type             = "n1-standard-32" # 32 CPU / 120 GB Memory
      min_count                = "1"
    },
  ]

  node_pools_tags = {
    all = []
    my_node_pool = [
      "allow-k8s-services-internal",
      "allow-k8s-services-external",
    ]
  }

  node_pools_labels = {
    all = {}
    my_node_pool = {}
  }

  node_pools_taints = {
    all = []
    my_node_pool = []
  }

  non_masquerade_cidrs = [
    "${data.google_compute_subnetwork.my_subnet.secondary_ip_range.0.ip_cidr_range}",
    "${data.google_compute_subnetwork.my_subnet.secondary_ip_range.1.ip_cidr_range}",
  ]

  stub_domains         {
    "some_domain_1" = ["some_ip","some_ip"]
    "some_domain_2" = ["some_ip","some_ip"]
    "some_domain_3" = ["some_ip","some_ip"]
  }
}

[Jberlinsky]

@sunggun-yu, thank you for your contribution! I'm glad this seems to have resolved the problems you encountered.

In attempting to reproduce this, I encountered a few additional changes that need to be made while we're in here. In particular, if your subnetwork and network are in different projects, this still won't work properly.

I've created #23 to track this issue, and expect to be working on this in the next couple days. Your change here will be incorporated into the resulting pull request. As such, I'm going to close this one.

Once again, thank you for reporting this!

[Jberlinsky]

@sunggun-yu, my apologies. The issues I referenced stem from a different set of circumstances. I'm going to run our test suite on your change and get it merged in if everything passes.

[Jberlinsky]

Looks good, merging!

[sunggun-yu]

@Jberlinsky, @morgante Thank you so much!!!