Use ./ prefix for inner/local worker pool modules

* Terraform v0.11 encouraged use of a "./" prefix for local module references
and Terraform v0.12 will require it
* https://www.terraform.io/docs/modules/sources.html#local-paths

Related: https://github.com/hashicorp/terraform/issues/19745

aws/container-linux/kubernetes/workers.tf

@@ -1,5 +1,5 @@
 module "workers" {
-  source = "workers"
+  source = "./workers"
   name   = "${var.cluster_name}"
 
   # AWS

aws/fedora-atomic/kubernetes/workers.tf

@@ -1,5 +1,5 @@
 module "workers" {
-  source = "workers"
+  source = "./workers"
   name   = "${var.cluster_name}"
 
   # AWS

azure/container-linux/kubernetes/workers.tf

@@ -1,5 +1,5 @@
 module "workers" {
-  source = "workers"
+  source = "./workers"
   name   = "${var.cluster_name}"
 
   # Azure

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

@@ -1,5 +1,5 @@
 module "workers" {
-  source       = "workers"
+  source       = "./workers"
   name         = "${var.cluster_name}"
   cluster_name = "${var.cluster_name}"
 

google-cloud/fedora-atomic/kubernetes/workers.tf

@@ -1,5 +1,5 @@
 module "workers" {
-  source       = "workers"
+  source       = "./workers"
   name         = "${var.cluster_name}"
   cluster_name = "${var.cluster_name}"