Verify delete security group response of V2 API

This patch adds the JSON schema for response status of Nova security group
delete API to block the backward incompatibility change in the future.

delete security group does not return the response body.
Response status of this API is 202.

Partially implements blueprint nova-api-attribute-test

Change-Id: I8ce635dfdb41cacaf433b7e14f0fe3b798ef839a
Merge "Verify delete security group response of V2 API"