switch documentation job to new PTI

Update .zuul.yaml to use PTI job, update tox.ini to use the common way
to run sphinx, update setup.cfg for handling warnings as errors.

Add new docs target to tox.ini and make it default target, the target is
needed by CI scripts.

Note that ossa does not work with python3, so the docs environment does
not use basepython. This needs a rework of doc/source/_exts/vmt.py.

Change-Id: I7196aab97167d857f0afdfe005d74c7f0f8f1073

.zuul.yaml

@@ -1,6 +1,6 @@
 - project:
     templates:
-      - build-openstack-sphinx-docs
+      - build-openstack-docs-pti
     post:
       jobs:
         - publish-security

setup.cfg

@@ -12,6 +12,7 @@ home-page = http://www.openstack.org/
 all_files = 1
 build-dir = doc/build
 source-dir = doc/source
+warning-is-error = 1
 
 [pbr]
 warnerrors = True

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = venv
+envlist = docs
 minversion = 1.6
 skipsdist = True
 
@@ -8,7 +8,13 @@ usedevelop = True
 install_command = pip install -U {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
 
+[testenv:docs]
+# The repo does not work with python3 yet, so no basepypthon set
+# to python3.
+deps = -r{toxinidir}/test-requirements.txt
+commands = sphinx-build -W -b html -d doc/build/doctrees doc/source doc/build/html
+
 [testenv:venv]
 basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
-commands =python setup.py build_sphinx
+commands = {[testenv:docs]commands}