Update docs job

build-openstack-sphinx-docs jobs are obsolete since some time,
use the newer build-openstack-docs-pti jobs instead - using
a template.

Update tox.ini to use proper sphinx-build invocation.

Change-Id: Idfa081711a24a6076e8b9a0ca770423d6fa62f94

.zuul.yaml

@@ -59,6 +59,7 @@
 
 - project:
     templates:
+      - build-openstack-docs-pti
       - check-requirements
       - tempest-plugin-jobs
     check:
@@ -68,11 +69,9 @@
             branches: ^(?!stable/(newton|ocata)).*$
         - mistral-devstack-kombu:
             branches: ^(?!stable/newton).*$
-        - build-openstack-sphinx-docs
     gate:
       queue: mistral
       jobs:
         - mistral-devstack
         - mistral-devstack-non-apache
         - mistral-devstack-kombu
-        - build-openstack-sphinx-docs

tox.ini

@@ -36,7 +36,7 @@ commands =
 
 [testenv:docs]
 basepython = python3
-commands = python setup.py build_sphinx
+commands = sphinx-build -W -d doc/build/doctrees -b html doc/source/ doc/build/html
 
 [testenv:releasenotes]
 basepython = python3