Add storage account param

packer/acstack.json

@@ -20,7 +20,7 @@
         "{{user `resource_group_name`}}",
       "capture_container_name": "acs-vhds",
       "capture_name_prefix": "acstack-{{timestamp}}",
-      "storage_account": "acstackimages",
+      "storage_account": "{{user `storage_account_name`}}",
 
       "os_type": "Linux",
       "image_publisher": "Canonical",

packer/settings-example.json

@@ -5,6 +5,7 @@
   "subscription_id": "",
   "resource_group_name": "ACStackImages",
   "managed_image_resource_group_name": "ACStackImages",
+  "storage_account_name": "",
   "location": "West US 2",
   "vm_size": "Standard_D2_v2"
 }