Add documentation for glance api

Added links for available params for glance v2 api.

Change-Id: I25d32ba3f2ebabc8132470d098ca2703c9f9eac6
diff --git a/tempest/lib/services/image/v2/namespaces_client.py b/tempest/lib/services/image/v2/namespaces_client.py
index 97400e1..5bd096d 100644
--- a/tempest/lib/services/image/v2/namespaces_client.py
+++ b/tempest/lib/services/image/v2/namespaces_client.py
@@ -58,6 +58,11 @@
         return rest_client.ResponseBody(resp, body)
 
     def delete_namespace(self, namespace):
+        """Delete a namespace.
+
+        Available params: http://developer.openstack.org/
+                          api-ref-image-v2.html#deleteNamespace-v2
+        """
         url = 'metadefs/namespaces/%s' % namespace
         resp, _ = self.delete(url)
         self.expected_success(204, resp.status)