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: Id80bab700d0535b919be6b8f42e0c1561557e45e
Closes-Bug: #1526170

setup.cfg

@@ -19,7 +19,7 @@ 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]
 packages =

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py34,py33,py27,pep8
+envlist = py34,py27,pep8
 minversion = 1.6
 skipsdist = True