Only run build-openstack-sphinx-docs on stable branches

We should not be using this on master. Also update it to pin to
python2 to get ready for zuul-jobs changing the default for
sphinx to python3.

Update descriptions to make clear that rocky was the last release
this is supported.

Change-Id: Ib896713623f58a8164d1a2e5f49dc5d316e292b9

zuul.d/jobs.yaml

@@ -6,8 +6,8 @@
 - job:
     name: build-openstack-sphinx-docs
     parent: build-sphinx-docs
+    branches: ^stable/(ocata|pike|queens|rocky).*$
     nodeset: ubuntu-xenial
-    branches: ^(?!driverfixes/).*$
     description: |
       Builds documentation using Sphinx per a previous version of the
       OpenStack PTI and then
@@ -17,7 +17,7 @@
       can be examined if desired, and also validates htaccess files
       using the whereto tool.
 
-      This job is obsolete and should not be used anymore since rocky, use
+      This job is obsolete and is not supported on branches after rocky, use
       :zuul:job:`openstack-tox-docs` instead.
     success-url: html/
     required-projects:
@@ -31,6 +31,7 @@
       - zuul: zuul/zuul-jobs
     vars:
       constraints_file: '{{ ansible_user_dir }}/src/opendev.org/openstack/requirements/upper-constraints.txt'
+      sphinx_python: python2
 
 - job:
     name: tox-py35-on-zuul

zuul.d/project-templates.yaml

@@ -35,7 +35,9 @@
     description: |
       Runs legacy OpenStack doc build without publication jobs.
 
-      This template is deprecated and should only be used for older stable
+      This template is deprecated, it is only running on branches
+      until rocky. Use
+      :zuul:project_template:`build-openstack-docs-pti` for newer
       branches.
     check:
       jobs:
@@ -49,7 +51,9 @@
     description: |
       Runs legacy OpenStack doc build and publication jobs.
 
-      This template is deprecated and should only be used for older stable
+      This template is deprecated, it is only running on branches
+      until rocky. Use
+      :zuul:project_template:`publish-openstack-docs-pti` for newer
       branches.
     check:
       jobs: