Drop py33 support

"Python 3.3 support is being dropped since OpenStack Liberty."
written in following URL.
https://wiki.openstack.org/wiki/Python3

And already the infra team and the oslo team are dropping py33
support from their projects.

Since we rely on oslo for a lot of our work, and depend on infra
for our CI, we should drop py33 support too.

Change-Id: Ic3bfd32822a5e55d6d056af163075d9b3bdaabd4
Closes-Bug: #1526170

setup.cfg

@@ -17,7 +17,6 @@ classifier =
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.3
     Programming Language :: Python :: 3.4
 
 [files]

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 # py3 first to avoid .testrepository incompatibility
-envlist = py33,py34,py27,pypy,pep8
+envlist = py34,py27,pypy,pep8
 minversion = 1.6
 skipsdist = True