Verify delete-Floating-IP-Bulk Nova API attributes

This patch adds the JSON schema for Nova V2 delete-Floating-IP-Bulk
API response and validate the response with added JSON schema
to block the backward incompatibility change in the future.

The response body of delete-Floating-IP-Bulk V2 API is below:

{
    "floating_ips_bulk_delete": "192.168.1.0/24"
}

Partially implements blueprint nova-api-attribute-test

Change-Id: Id48ba7129d97c3691f8e61375f4205b1587d385b
Merge "Verify delete-Floating-IP-Bulk Nova API attributes"