Validate get_instance_usage_audit_log Nova V2 API

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

Response body of V2 GET instance_usage_audit_log is below-

{
    "instance_usage_audit_log": {
        "hosts_not_run": [
            "%(hostid)s"
        ],
        "log": {},
        "num_hosts": 1,
        "num_hosts_done": 0,
        "num_hosts_not_run": 1,
        "num_hosts_running": 0,
        "overall_status": "0 of 1 hosts done. 0 errors.",
        "period_beginning": "%(timestamp)s",
        "period_ending": "%(timestamp)s",
        "total_errors": 0,
        "total_instances": 0
    }
}

Partially implements blueprint nova-api-attribute-test

Change-Id: I0112c331e83ade95f3a6a9d5e5434d76703a09eb
Merge "Validate get_instance_usage_audit_log Nova V2 API"