Verify the response attributes of 'create-aggregate' API

This patch verifies the response attributes of 'create-aggregate'.
The response attributes of v2 and v3 are the same:
{
    "aggregate": {
        "availability_zone": "nova",
        "created_at": "2012-10-01T18:50:27.781065",
        "deleted": false,
        "deleted_at": null,
        "id": 1,
        "name": "name",
        "updated_at": null
    }
}
The status_code is different:
  v2 -> 200
  v3 -> 201
This patch also fixed a typo bug in the compute/aggregates.py

Partially implements blueprint nova-api-attribute-test

Change-Id: I584ee2b9ac6033fb365a8dadd4e3844b1c37edb2
Merge "Verify the response attributes of 'create-aggregate' API"