Create project-templates for sphinx building with python3

Let's add these to make publishing of e.g. governance and release repo
easy.

Change-Id: Iaa2c9869b3e27b8b79ad42ca35ff148be4c71fd7
Depends-On: Idd7caf7d88b56d61872906027b4ce7d743572ded
Needed-By: I091d6731a2fb4c2ed4b432abaccaabd6852f0d0f

zuul.d/project-templates.yaml

@@ -19,6 +19,23 @@
       jobs:
         - build-openstack-sphinx-docs
 
+- project-template:
+    name: build-openstack-sphinx-docs-python3
+    description: |
+      Runs normal OpenStack PTI doc build without publication jobs.
+
+      Builds the docs using Sphinx with Python3.
+    check:
+      jobs:
+        - build-openstack-sphinx-docs:
+            vars:
+              sphinx_python: python3
+    gate:
+      jobs:
+        - build-openstack-sphinx-docs:
+            vars:
+              sphinx_python: python3
+
 - project-template:
     name: publish-openstack-sphinx-docs
     description: |
@@ -33,6 +50,26 @@
       jobs:
         - publish-openstack-sphinx-docs
 
+- project-template:
+    name: publish-openstack-sphinx-docs-python3
+    description: |
+      Runs normal OpenStack PTI doc build and publication jobs.
+
+      Builds the docs using Sphinx with Python3.
+    check:
+      jobs:
+        - build-openstack-sphinx-docs:
+            vars:
+              sphinx_python: python3
+    gate:
+      jobs:
+        - build-openstack-sphinx-docs:
+            vars:
+              sphinx_python: python3
+    post:
+      jobs:
+        - publish-openstack-sphinx-docs-python3
+
 - project-template:
     name: publish-openstack-sphinx-docs-horizon
     description: |