Ship the default image schema in the client

Now that we have stable branches for clients, it's easier to keep track
of the current default image's schema in Glance and update it
respectively. This patch adds the current image schema, including the
schema-properties.

One good reason to do this is to be able to react when a running Glance
instance is not around to be introspected. It's really unfortunate that
things like help text can't be rendered when there image schema is not
available in the system.

We could keep the schema in a json file but rather than shipping data
files with glanceclient we can just have it in the python modules.

Change-Id: I9b8cc1d18d6717ccf991fb8149ab13c06d653ee4
Closes-bug: #1481729

glanceclient/v2/shell.py

@@ -19,6 +19,7 @@ from glanceclient.common import progressbar
 from glanceclient.common import utils
 from glanceclient import exc
 from glanceclient.v2 import image_members
+from glanceclient.v2 import image_schema
 from glanceclient.v2 import images
 from glanceclient.v2 import tasks
 import json
@@ -36,6 +37,8 @@ def get_image_schema():
             with open(schema_path, "r") as f:
                 schema_raw = f.read()
                 IMAGE_SCHEMA = json.loads(schema_raw)
+        else:
+            return image_schema._BASE_SCHEMA
     return IMAGE_SCHEMA