Verify attributes through Nova os-security-groups API

This patch adds checks whether a response of Nova security group
get/create/update API includes the attributes to block the backward
incompatibility change in the future.

The response body of v2 get/create/update API is the below:
{
    "security_group": {
        "id": 10,
        "name": "sg1",
        "tenant_id": "bd9a4c2ed39e49f4aa525e99a5f92454",
        "rules": [],
        "description": "Test security group."
    }
}

Partially implements blueprint nova-api-attribute-test

Change-Id: I7888e1e483ff77adcaf2bd9a38676bd2075e1305
Merge "Verify attributes through Nova os-security-groups API"