python3: Introduce py33 to tox.ini

Introduce py33 to tox.ini to make testing with
python3 easier.

Change-Id: I7a775ac51e0bc0a5929184af47d51ea1cc4e3219
Signed-off-by: Chuck Short <chuck.short@canonical.com>

Author: Chuck Short

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py26,py27,pep8
+envlist = py26,py27,py33,pep8
 
 [testenv]
 setenv = VIRTUAL_ENV={envdir}