Validate Volume attributes of Nova POST & GET API

This patch adds the JSON schema and validate the response
of Nova POST & GET Volume APIs with JSON schema to block
the backward incompatibility change in the future.

The response body of Nova POST & GET Volume is the following:

{
    "volume": {
        "attachments": [
            {
                "device": "/",
                "id": "a26887c6-c47b-4654-abb5-dfadf7d3f803",
                "serverId": "3912f2b4-c5ba-4aec-9165-872876fe202e",
                "volumeId": "a26887c6-c47b-4654-abb5-dfadf7d3f803"
            }
        ],
        "availabilityZone": "zone1:host1",
        "createdAt": "2013-02-18T14:51:18.528085",
        "displayDescription": "Volume Description",
        "displayName": "Volume Name",
        "id": "a26887c6-c47b-4654-abb5-dfadf7d3f803",
        "metadata": {},
        "size": 100,
        "snapshotId": null,
        "status": "in-use",
        "volumeType": "Backup"
    }
}

Partially implements blueprint nova-api-attribute-test

Change-Id: I7b98b375b87577d9bb9cf80b2fedd3b65ad0cd72
Fix issue with pep8 gate job

Since test-scenario is working on import level the configuration is
may not in place. This causes an error in the pep8 job.

Change-Id: I761c82338eb513a4870b2e3cdf6ab7e98790b6f4
Implements: bug 1291826
Merge "Fix issue with pep8 gate job"
Merge "Validate Volume attributes of Nova POST & GET API"