Verify V2 list server_group API attributes

This patch adds the JSON schema for Nova V2 list
server_group API response and validate the response with added
JSON schema to block the backward incompatibility change in the future.

The response body of List server_group V2 API is given below:

{
    "server_groups": [
        {
            "id": "616fb98f-46ca-475e-917e-2563e5a8cd19",
            "name": "test",
            "policies": ["anti-affinity"],
            "members": [],
            "metadata": {}
        }
    ]
}

Partially implements blueprint nova-api-attribute-test

Change-Id: I554237d9b66b42ea75ef3b47c8a9038c80b3cfb5
Merge "Verify V2 list server_group API attributes"