Nova instance config drive Metadata Definition

A nova Juno FFE landed to support setting the
img_config_drive property on images to require images
to be booted with a config drive. The Glance Metadata
Definitions should include this property.

See Nova Blueprint:
https://blueprints.launchpad.net/nova/+spec/config-drive-image-property

Change-Id: Iffc4d4f00f3677ed1fa41233ef6cfbc5c46d8602
Closes-bug: 1367981
(cherry picked from commit 0dd620c)

etc/metadefs/compute-instance-data.json

@@ -0,0 +1,27 @@
+{
+    "namespace": "OS::Compute::InstanceData",
+    "display_name": "Instance Config Data",
+    "description": "Instances can perform self-configuration based on data made available to the running instance. These properties affect instance configuration.",
+    "visibility": "public",
+    "protected": true,
+    "resource_type_associations": [
+        {
+            "name": "OS::Glance::Image"
+        },
+        {
+            "name": "OS::Cinder::Volume",
+            "properties_target": "image"
+        }
+    ],
+    "properties": {
+        "img_config_drive": {
+            "title": "Config Drive",
+            "description": "Set this property on images to mandatory to require Nova to use a config drive when booting the image. OpenStack can be configured to write metadata to a special configuration drive that will be attached to the instance when it boots. The instance can retrieve any information from the config drive. One use case for the config drive is to pass network configuration information to the instance. See also: http://docs.openstack.org/user-guide/content/config-drive.html",
+            "type": "string",
+            "enum": [
+                "optional",
+                "mandatory"
+            ]
+        }
+    }
+}