fixed the bug 983856. Pep8 complient made

Change-Id: I6956020b9829fb02ce09b129d44b378f4b0c18c1
diff --git a/tempest/tests/test_volumes_list.py b/tempest/tests/test_volumes_list.py
index 4a4c7d1..01ce394 100644
--- a/tempest/tests/test_volumes_list.py
+++ b/tempest/tests/test_volumes_list.py
@@ -25,7 +25,8 @@
             cls.volume_list.append(volume)
             cls.volume_id_list.append(volume['id'])
 
-    def teardown(cls):
+    @classmethod
+    def tearDownClass(cls):
         #Delete the created Volumes
         for i in range(3):
             resp, _ = cls.client.delete_volume(cls.volume_id_list[i])