use assertIsNotNone instead of assertNotEqual(*, None)

Change-Id: I8c7891117c9c594d44479a33b406e8ab7711f304
diff --git a/tempest/api/compute/servers/test_virtual_interfaces.py b/tempest/api/compute/servers/test_virtual_interfaces.py
index 2a5be8c..e5ea30e 100644
--- a/tempest/api/compute/servers/test_virtual_interfaces.py
+++ b/tempest/api/compute/servers/test_virtual_interfaces.py
@@ -45,7 +45,7 @@
         # for a given server_id
         resp, output = self.client.list_virtual_interfaces(self.server_id)
         self.assertEqual(200, resp.status)
-        self.assertNotEqual(output, None)
+        self.assertIsNotNone(output)
         virt_ifaces = output
         self.assertNotEqual(0, len(virt_ifaces['virtual_interfaces']),
                             'Expected virtual interfaces, got 0 interfaces.')