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: Idfd9818434481ede85ff8e746893ac7e27fcb333

setup.cfg

@@ -18,6 +18,7 @@ classifier =
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.4
+    Programming Language :: Python :: 3.5
 
 [entry_points]
 oslo.config.opts =

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 1.6
-envlist = py34,py27,pep8
+envlist = py35,py34,py27,pep8
 skipsdist = True
 
 [testenv]