Add Python 3.5 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: I006650a6e67fd54c4823ef560ee26322c2c13428

setup.cfg

@@ -19,6 +19,7 @@ classifier =
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.4
+    Programming Language :: Python :: 3.5
     Topic :: Software Development :: Libraries
     Topic :: System :: Distributed Computing
 

tox.ini

@@ -5,6 +5,7 @@ envlist = cover,
     pep8,
     py27,
     py34,
+    py35,
     pylint,
     update-states