Fix calls to call_until_true

Some tests use call_until_true, but don't check the returned value. If
False, the check isn't actually correct.

Change-Id: I6625a2e57d1d1c1ac03647786c210a9b57490562
diff --git a/functional/test_notifications.py b/functional/test_notifications.py
index 924ef0c..69029a7 100644
--- a/functional/test_notifications.py
+++ b/functional/test_notifications.py
@@ -180,12 +180,14 @@
                                 auto_declare=False):
 
             requests.post(scale_up_url, verify=self.verify_cert)
-            test.call_until_true(20, 0, self.consume_events, handler, 2)
+            self.assertTrue(
+                test.call_until_true(20, 0, self.consume_events, handler, 2))
             notifications += handler.notifications
 
             handler.clear()
             requests.post(scale_down_url, verify=self.verify_cert)
-            test.call_until_true(20, 0, self.consume_events, handler, 2)
+            self.assertTrue(
+                test.call_until_true(20, 0, self.consume_events, handler, 2))
             notifications += handler.notifications
 
         self.assertEqual(2, notifications.count(ASG_NOTIFICATIONS[0]))