Verify the response attributes of 'list_aggregates'

This patch verifies the response attributes of list_aggregates.
The response body of v2 and v3 API has the same format:

"aggregates": [
    {
        "availability_zone": "nova",
        "created_at": "2012-11-16T06:22:23.361359",
        "deleted": false,
        "deleted_at": null,
        "hosts": [],
        "id": 1,
        "metadata": {
            "availability_zone": "nova"
        },
        "name": "name",
        "updated_at": null
    }
]

Partially implements blueprint nova-api-attribute-test

Change-Id: If4c09929f3e9d3fd743aad2b727a74834fdbf8fd
diff --git a/tempest/services/compute/json/aggregates_client.py b/tempest/services/compute/json/aggregates_client.py
index 700a29b..ccb85c4 100644
--- a/tempest/services/compute/json/aggregates_client.py
+++ b/tempest/services/compute/json/aggregates_client.py
@@ -15,6 +15,7 @@
 
 import json
 
+from tempest.api_schema.compute import aggregates as schema
 from tempest.common import rest_client
 from tempest import config
 from tempest import exceptions
@@ -32,6 +33,7 @@
         """Get aggregate list."""
         resp, body = self.get("os-aggregates")
         body = json.loads(body)
+        self.validate_response(schema.list_aggregates, resp, body)
         return resp, body['aggregates']
 
     def get_aggregate(self, aggregate_id):