Tests Cleanup: Fix missing calls to setUpClass/tearDownClass.

Continuation/Part 2 of https://gerrit.fd.io/r/#/c/17092/

Change-Id: Id0122d84eaf2c05d29e5be63a594d5e528ee7c9a
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>
diff --git a/test/test_ip6_vrf_multi_instance.py b/test/test_ip6_vrf_multi_instance.py
index 4b4a9e4..45c192d 100644
--- a/test/test_ip6_vrf_multi_instance.py
+++ b/test/test_ip6_vrf_multi_instance.py
@@ -160,6 +160,10 @@
             super(TestIP6VrfMultiInst, cls).tearDownClass()
             raise
 
+    @classmethod
+    def tearDownClass(cls):
+        super(TestIP6VrfMultiInst, cls).tearDownClass()
+
     def setUp(self):
         """
         Clear trace and packet infos before running each test.