Check  get_vnc_console attributes of Nova APIs

This patch adds the JSON schema for Nova V2 & V3 get_vnc_console
server action APIs response and validate the response with added
JSON schema to block the backward incompatibility change in the future.

The response body of get_vnc_console V2 & V3 APIs is same and given
below:

{
    "console": {
        "type": "novnc",
        "url": "http://127.0.0.1:6080/vnc_auto.html?token=%(uuid)s"
    }
}

Partially implements blueprint nova-api-attribute-test

Change-Id: Idfcdcd84207d5958011b7a748e59f6414000bbc9
Merge "Check  get_vnc_console attributes of Nova APIs"