Add tempest tests for os-aggregate update

Add tests of os-aggregate update for API 'os-aggregates/{aggregate_id}'

Change-Id: I1624c366faa9a97461b68c7408e309a658c4cb83
diff --git a/tempest/services/compute/json/aggregates_client.py b/tempest/services/compute/json/aggregates_client.py
index 7ae1eee..75ce9ff 100644
--- a/tempest/services/compute/json/aggregates_client.py
+++ b/tempest/services/compute/json/aggregates_client.py
@@ -52,6 +52,19 @@
         body = json.loads(body)
         return resp, body['aggregate']
 
+    def update_aggregate(self, aggregate_id, name, availability_zone=None):
+        """Update a aggregate."""
+        put_body = {
+            'name': name,
+            'availability_zone': availability_zone
+        }
+        put_body = json.dumps({'aggregate': put_body})
+        resp, body = self.put('os-aggregates/%s' % str(aggregate_id),
+                              put_body, self.headers)
+
+        body = json.loads(body)
+        return resp, body['aggregate']
+
     def delete_aggregate(self, aggregate_id):
         """Deletes the given aggregate."""
         return self.delete("os-aggregates/%s" % str(aggregate_id))