Rename worker pool modules' count variable to worker_count

* This change affects users who use worker pools on AWS, GCP, or
Azure with a Container Linux derivative
* Rename worker pool modules' `count` variable to `worker_count`,
because `count` will be a reserved variable name in Terraform v0.12

azure/container-linux/kubernetes/workers.tf

@@ -9,7 +9,7 @@ module "workers" {
   security_group_id       = "${azurerm_network_security_group.worker.id}"
   backend_address_pool_id = "${azurerm_lb_backend_address_pool.worker.id}"
 
-  count    = "${var.worker_count}"
+  worker_count    = "${var.worker_count}"
   vm_type  = "${var.worker_type}"
   os_image = "${var.os_image}"
   priority = "${var.worker_priority}"

azure/container-linux/kubernetes/workers/variables.tf

@@ -32,7 +32,7 @@ variable "backend_address_pool_id" {
 
 # instances
 
-variable "count" {
+variable "worker_count" {
   type        = "string"
   default     = "1"
   description = "Number of instances"

azure/container-linux/kubernetes/workers/workers.tf

@@ -15,7 +15,7 @@ resource "azurerm_virtual_machine_scale_set" "workers" {
   sku {
     name     = "${var.vm_type}"
     tier     = "standard"
-    capacity = "${var.count}"
+    capacity = "${var.worker_count}"
   }
 
   # boot
@@ -87,9 +87,9 @@ resource "azurerm_monitor_autoscale_setting" "workers" {
     name = "default"
 
     capacity {
-      minimum = "${var.count}"
-      default = "${var.count}"
-      maximum = "${var.count}"
+      minimum = "${var.worker_count}"
+      default = "${var.worker_count}"
+      maximum = "${var.worker_count}"
     }
   }
 }