Use new Azure subnet to set address_prefixes list

* Update Azure subnet `address_prefix` to `azure_prefixes` list
* Fix warning that `address_prefix` is deprecated
* Require `terraform-provider-azurerm` v2.8.0+ (action required)

Rel: hashicorp/terraform-provider-azurerm#6493

controllers.tf

@@ -66,9 +66,9 @@ resource "azurerm_linux_virtual_machine" "controllers" {
     for_each = local.flavor == "flatcar" ? [1] : []
 
     content {
-      name = local.channel
+      name      = local.channel
       publisher = "kinvolk"
-      product = "flatcar-container-linux-free"
+      product   = "flatcar-container-linux-free"
     }
   }
 

network.tf

@@ -21,7 +21,7 @@ resource "azurerm_subnet" "controller" {
 
   name                 = "controller"
   virtual_network_name = azurerm_virtual_network.network.name
-  address_prefix       = cidrsubnet(var.host_cidr, 1, 0)
+  address_prefixes     = [cidrsubnet(var.host_cidr, 1, 0)]
 }
 
 resource "azurerm_subnet_network_security_group_association" "controller" {
@@ -34,7 +34,7 @@ resource "azurerm_subnet" "worker" {
 
   name                 = "worker"
   virtual_network_name = azurerm_virtual_network.network.name
-  address_prefix       = cidrsubnet(var.host_cidr, 1, 1)
+  address_prefixes     = [cidrsubnet(var.host_cidr, 1, 1)]
 }
 
 resource "azurerm_subnet_network_security_group_association" "worker" {

versions.tf

@@ -3,7 +3,7 @@
 terraform {
   required_version = "~> 0.12.6"
   required_providers {
-    azurerm  = "~> 2.0"
+    azurerm  = "~> 2.8"
     ct       = "~> 0.3"
     template = "~> 2.1"
     null     = "~> 2.1"

workers/workers.tf

@@ -37,9 +37,9 @@ resource "azurerm_linux_virtual_machine_scale_set" "workers" {
     for_each = local.flavor == "flatcar" ? [1] : []
 
     content {
-      name = local.channel
+      name      = local.channel
       publisher = "kinvolk"
-      product = "flatcar-container-linux-free"
+      product   = "flatcar-container-linux-free"
     }
   }