Add Python3.5 classifier and venv

Now that there is a passing gate job, we can claim support for Python 3.5
in the classifier. This patch also adds the convenience py35 venv.

Change-Id: I29cab82225675fbb4e2f1701067b26e4a632b851

setup.cfg

@@ -19,6 +19,8 @@ classifier =
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.4
+    Programming Language :: Python :: 3.5
+
 
 [global]
 setup-hooks =

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 distribute = False
-envlist = py34,py27,pep8
+envlist = py35,py34,py27,pep8
 minversion = 1.8
 skipsdist = True