fix example (#176)

quickstart/201-web-app-docker-acr/app_service.tf

@@ -1,27 +1,30 @@
-
 resource "azurerm_app_service_plan" "default" {
-  name                = "${var.name}-plan"
-  location            = "${azurerm_resource_group.default.location}"
-  resource_group_name = "${azurerm_resource_group.default.name}"
+  name                = "${random_pet.prefix.id}-plan"
+  location            = azurerm_resource_group.default.location
+  resource_group_name = azurerm_resource_group.default.name
   kind                = "Linux"
 
   # Reserved must be set to true for Linux App Service Plans
   reserved = true
 
   sku {
-    tier = "${var.plan_tier}"
-    size = "${var.plan_sku}"
+    tier = var.plan_tier
+    size = var.plan_sku
   }
 }
 
-resource "azurerm_app_service" "default" {
-  name                = "${var.dns_prefix}-${var.name}-${var.environment}-app"
-  location            = "${azurerm_resource_group.default.location}"
-  resource_group_name = "${azurerm_resource_group.default.name}"
-  app_service_plan_id = "${azurerm_app_service_plan.default.id}"
+resource "azurerm_app_service" "main" {
+  name                = "${var.dns_prefix}-${random_pet.prefix.id}-${var.environment}-app"
+  location            = azurerm_resource_group.default.location
+  resource_group_name = azurerm_resource_group.default.name
+  app_service_plan_id = azurerm_app_service_plan.default.id
+
+  identity {
+    type = "SystemAssigned"
+  }
 
   site_config {
     always_on        = true
     linux_fx_version = "DOCKER|nginxdemos/hello"
   }
-}
+}