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: Iaec0c9e88cb38ab876b5bc957f53989615cab246
diff --git a/setup.cfg b/setup.cfg
index 2a3000d..76bed2b 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -17,6 +17,7 @@
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.4
+    Programming Language :: Python :: 3.5
 
 [files]
 packages =