Add compute API response schema validation for 2.71

The 2.71 compute API includes the "server_groups" parameter
in the response to the following APIs:

- GET /servers/{server_id} (show)
- PUT /servers/{server_id} (update)
- POST /servers/{server_id}/action (rebuild)

This will be used in an upcoming change to test attaching
and detaching the root volume of a shelved offloaded instance.

Change-Id: I612a15c475404ded0af15b6241b9ac8ec9fb8e26
4 files changed