Unsupported 'message' Exception attribute in PY3

 * Fix unsupported 'message' Exception attribute in PY3
   The 'message' attribute has been deprecated and removed from Python3.
   Use six.text_type(e) instead of e.message. For more details, please check [1]:
   [1] https://www.python.org/dev/peps/pep-0352/
 * Add hacking to prevent this from happening in the future.

Change-Id: Id40000c2c453815b04a7d2fd765e19997291d8e3
diff --git a/HACKING.rst b/HACKING.rst
index e5f45ac..446d865 100644
--- a/HACKING.rst
+++ b/HACKING.rst
@@ -24,6 +24,7 @@
 - [T114] Check that tempest.lib does not use tempest config
 - [T115] Check that admin tests should exist under admin path
 - [N322] Method's default argument shouldn't be mutable
+- [T116] Unsupported 'message' Exception attribute in PY3
 
 Test Data/Configuration
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