TestServerAdvancedOps server leaking

When added the testresources added as base class the resource variable usage
changed, and it renamed to os_resources in the other places.

TestServerAdvancedOps still want to use the old variable,
 however the base class has proper tearDownClass method.

Let the TestServerAdvancedOps to use the base class's tearDownClass.

Fixes Bug 1157306

Change-Id: I9bc1c90d526865cafbc6fbf71172aae10e95cb7d
diff --git a/tempest/scenario/test_server_advanced_ops.py b/tempest/scenario/test_server_advanced_ops.py
index 109aaa5..6202e91 100644
--- a/tempest/scenario/test_server_advanced_ops.py
+++ b/tempest/scenario/test_server_advanced_ops.py
@@ -45,11 +45,6 @@
             msg = "Skipping test - flavor_ref and flavor_ref_alt are identical"
             raise cls.skipException(msg)
 
-    @classmethod
-    def tearDownClass(cls):
-        for thing in cls.resources:
-            thing.delete()
-
     def test_resize_server_confirm(self):
         # We create an instance for use in this test
         i_name = rand_name('instance')