bisect-kit: improve output message slightly

Change 'old' and 'new' to 'old behavior' and 'new behavior'. This should
be easier to understand for users.

BUG=b:117860228
TEST=None

Change-Id: I342895633f1ab24d5e9c3f3a0af8860f76f57fcb
Reviewed-on: https://chromium-review.googlesource.com/1421587
Commit-Ready: Kuang-che Wu <kcwu@chromium.org>
Tested-by: Kuang-che Wu <kcwu@chromium.org>
Reviewed-by: Chung-yih Wang <cywang@chromium.org>
diff --git a/bisect_kit/errors.py b/bisect_kit/errors.py
index f29f4d2..501b687 100644
--- a/bisect_kit/errors.py
+++ b/bisect_kit/errors.py
@@ -60,18 +60,18 @@
     super(VerificationFailed, self).__init__(msg)
 
 
-class VerifyOldFailed(VerificationFailed):
+class VerifyOldBehaviorFailed(VerificationFailed):
   """Old version does not behave as old."""
 
   def __init__(self, rev, bad_times=1):
-    super(VerifyOldFailed, self).__init__(rev, 'old', 'new', bad_times)
+    super(VerifyOldBehaviorFailed, self).__init__(rev, 'old', 'new', bad_times)
 
 
-class VerifyNewFailed(VerificationFailed):
+class VerifyNewBehaviorFailed(VerificationFailed):
   """New version does not behave as new."""
 
   def __init__(self, rev, bad_times=1):
-    super(VerifyNewFailed, self).__init__(rev, 'new', 'old', bad_times)
+    super(VerifyNewBehaviorFailed, self).__init__(rev, 'new', 'old', bad_times)
 
 
 class UnableToProceed(Exception):