Add support for pushing and pulling schema 2 manifests with remote layers

This is required for windows image support

test/registry/protocol_v1.py

@@ -93,7 +93,6 @@ class V1Protocol(RegistryProtocol):
 
     # GET /v1/repositories/{namespace}/{repository}/tags
     image_ids = self.conduct(session, 'GET', prefix + 'tags', headers=headers).json()
-    assert len(image_ids.values()) >= len(tag_names)
 
     for tag_name in tag_names:
       if tag_name not in image_ids:
@@ -145,6 +144,8 @@ class V1Protocol(RegistryProtocol):
     headers['Authorization'] = 'token ' + result.headers['www-authenticate']
 
     for image in images:
+      assert image.urls is None
+
       # PUT /v1/images/{imageID}/json
       image_json_data = {'id': image.id}
       if image.size is not None: