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

Update docs tox environment to build ChangeLog file when using tox -e
docs.

Change-Id: If68bdb33bbf0727d699268d9de511790c8a048be
Story: #2002586
Task: #24320

.zuul.yaml

@@ -6,8 +6,8 @@
       - openstack-python35-jobs
       - openstack-pypy-jobs-nonvoting
       - lib-forward-testing
-      - publish-openstack-sphinx-docs
-      - release-notes-jobs
+      - publish-openstack-docs-pti
+      - release-notes-jobs-python3
     check:
       jobs:
         - osc-functional-devstack:

tox.ini

@@ -53,6 +53,8 @@ deps =
   -r{toxinidir}/doc/requirements.txt
 commands =
     sphinx-apidoc -o doc/api osc_lib osc_lib/tests
+    # Create ChangeLog file
+    python setup.py sdist
     sphinx-build -a -E -W -d doc/build/doctrees -b html doc/source doc/build/html
 
 [testenv:releasenotes]