Fix test_project_create_with_parent

The cleanup was being done in the wrong order, we can never try
to delete a project with children.

Change-Id: Ib2a3934d0698a1223e368d03f5671989120901f7
diff --git a/tempest/api/identity/admin/v3/test_projects.py b/tempest/api/identity/admin/v3/test_projects.py
index b53cfae..bee77df 100644
--- a/tempest/api/identity/admin/v3/test_projects.py
+++ b/tempest/api/identity/admin/v3/test_projects.py
@@ -83,7 +83,7 @@
         project = self.projects_client.create_project(
             project_name, domain_id=domain_id,
             parent_id=root_project_id)['project']
-        self.data.projects.append(project)
+        self.addCleanup(self.projects_client.delete_project, project['id'])
         parent_id = project['parent_id']
         self.assertEqual(project_name, project['name'])
         self.assertEqual(root_project_id, parent_id)