Update testing jobs

Remove py35 testing, for train py35 is not supported anymore.

Update docs environment to use sphinx-build directly following PTI.

Change-Id: Idd120c50f3205be116a22af83029b1560876fa36

.zuul.yaml

@@ -1,7 +1,6 @@
 - project:
     templates:
       - openstack-python-jobs
-      - openstack-python35-jobs
       - openstack-python36-jobs
       - openstack-python37-jobs
       - publish-openstack-docs-pti

setup.cfg

@@ -16,7 +16,8 @@ classifier =
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.5
+    Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
 
 [files]
 packages =

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 2.0
-envlist = py35,py37,py27,pep8
+envlist = py36,py37,py27,pep8
 skipsdist = True
 
 [testenv]
@@ -36,7 +36,7 @@ commands =
 
 [testenv:docs]
 basepython = python3
-commands = python setup.py build_sphinx
+commands = sphinx-build -W -b html -d doc/build/doctrees doc/source doc/build/html
 
 [testenv:releasenotes]
 basepython = python3