Verify get_instance_action attributes of Nova API

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

The response body of get_instance_actions V2 API is below:
{
    "instanceAction": {
        "action": "reboot",
        "instance_uuid": "b48316c5-71e8-45e4-9884-6c78055b9b13",
        "request_id": "req-3293a3f1-b44c-4609-b8d2-d81b105636b8",
        "user_id": "789",
        "project_id": "147",
        "start_time": "2012-12-05 00:00:00.000000",
        "message": "",
        "events": [
            {
                "event": "schedule",
                "start_time": "2012-12-05 01:00:02.000000",
                "finish_time": "2012-12-05 01:02:00.000000",
                "result": "Success",
                "traceback": ""
            },
            {
                "event": "compute_create",
                "start_time": "2012-12-05 01:03:00.000000",
                "finish_time": "2012-12-05 01:04:00.000000",
                "result": "Success",
                "traceback": ""
            }
        ]
    }
}

The response body of get_instance_actions V3 API is below:
{
    "server_action": {
        "action": "reboot",
        "server_uuid": "b48316c5-71e8-45e4-9884-6c78055b9b13",
        "request_id": "req-3293a3f1-b44c-4609-b8d2-d81b105636b8",
        "user_id": "789",
        "project_id": "147",
        "start_time": "2012-12-05T00:00:00.000000",
        "message": "",
        "events": [
            {
                "event": "schedule",
                "start_time": "2012-12-05T01:00:02.000000",
                "finish_time": "2012-12-05T01:02:00.000000",
                "result": "Success",
                "traceback": ""
            },
            {
                "event": "compute_create",
                "start_time": "2012-12-05T01:03:00.000000",
                "finish_time": "2012-12-05T01:04:00.000000",
                "result": "Success",
                "traceback": ""
            }
        ]
    }
}

Partially implements blueprint nova-api-attribute-test

Change-Id: I7b0d64b1db19359e5ff81b7cbbebef0b11946a1b
Merge "Verify get_instance_action attributes of Nova API"