Use more specific asserts in tests

Instead of assertTrue and assertFalse use more specific asserts.
They are compatible with Python 2.7[1] and 3.4[2]

[1]: https://docs.python.org/2.7/library/unittest.html
[2]: https://docs.python.org/3.4/library/unittest.html

Change-Id: Ifee66714db561fb329911395b2cfdd90c689b609
diff --git a/functional/test_stack_events.py b/functional/test_stack_events.py
index 3638fab..d5a7fad 100644
--- a/functional/test_stack_events.py
+++ b/functional/test_stack_events.py
@@ -74,7 +74,7 @@
                 stack_event.resource_name)
 
             # Resource events are a subset of the original stack event list
-            self.assertTrue(len(resource_events) < len(stack_events))
+            self.assertLess(len(resource_events), len(stack_events))
 
             # Get the event details for each resource event
             for resource_event in resource_events: