switch documentation job to new PTI

This is a mechanically generated patch to switch the documentation
jobs to use the new PTI versions of the jobs as part of the
python3-first goal.

See the python3-first goal document for details:
https://governance.openstack.org/tc/goals/stein/python3-first.html

Fix tox doc environment so that this works:
* move doc8 to pep8 following PTI
* build doc dir, not api-ref

Change-Id: I57003bd81f8214f27e3ca95ea87bba24fd44191b
Story: #2002586
Task: #24346

.zuul.yaml

@@ -84,8 +84,8 @@
       - openstack-python-jobs
       - periodic-stable-jobs
       - check-requirements
-      - publish-openstack-sphinx-docs
-      - release-notes-jobs
+      - publish-openstack-docs-pti
+      - release-notes-jobs-python3
       - install-guide-jobs
     check:
       jobs:

tox.ini

@@ -26,7 +26,9 @@ commands = ostestr --concurrency 1 {posargs}
 
 [testenv:pep8]
 basepython = python3
-commands = flake8
+commands =
+  doc8 doc/source
+  flake8
 
 [testenv:genconfig]
 basepython = python3
@@ -53,11 +55,8 @@ commands = {posargs}
 basepython = python3
 deps =
   -r{toxinidir}/doc/requirements.txt
-  -r{toxinidir}/test-requirements.txt
-
 commands =
-  doc8 doc/source
-  sphinx-build -W -b html api-ref/source api-ref/build/html
+  sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:api-ref]
 basepython = python3