Verify Nova create & get Floating IP attributes

This patch adds the JSON schema for Nova create & get Floating IP
APIs response and validate the response with added JSON schema
to block the backward incompatibility change in the future.

The response body of create & get Floating IP APIs is below:

{
    "floating_ip": {
        "id": 1,
        "pool": "nova",
        "instance_id": null,
        "ip": "10.10.10.1",
        "fixed_ip": null,
    }
}

Partially implements blueprint nova-api-attribute-test

Change-Id: Ia1c2f856511e62d7a0da01ac78bd37383596198f
Merge "Verify Nova create & get Floating IP attributes"