Switch to newer openstackdocstheme and reno versions

Switch to openstackdocstheme 2.2.0 and reno 3.1.0 versions. Using
these versions will allow especially:
* Linking from HTML to PDF document
* Allow parallel building of documents
* Fix some rendering problems

Update Sphinx version as well.

openstackdocstheme renames some variables, so follow the renames
before the next release removes them. A couple of variables are also
not needed anymore, remove them.

Depends-On: https://review.opendev.org/728938
Change-Id: I3a57dfef23cee9dc4430f46063e89ffb54d0396c

doc/requirements.txt

@@ -2,7 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 # this is required for the docs build jobs
-sphinx>=1.8.0,!=2.1.0 # BSD
-openstackdocstheme>=1.20.0 # Apache-2.0
-reno>=2.5.0 # Apache-2.0
+sphinx>=2.0.0,!=2.1.0 # BSD
+openstackdocstheme>=2.2.0 # Apache-2.0
+reno>=3.1.0 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD

doc/source/conf.py

@@ -26,9 +26,9 @@ extensions = [
 ]
 
 # openstackdocstheme options
-repository_name = 'openstack/oslo.utils'
-bug_project = 'oslo.utils'
-bug_tag = ''
+openstackdocs_repo_name = 'openstack/oslo.utils'
+openstackdocs_bug_project = 'oslo.utils'
+openstackdocs_bug_tag = ''
 
 # autodoc generation is a bit aggressive and a nuisance when doing heavy
 # text edit cycles.

releasenotes/source/conf.py

@@ -40,9 +40,9 @@ extensions = [
 ]
 
 # openstackdocstheme options
-repository_name = 'openstack/oslo.utils'
-bug_project = 'oslo.utils'
-bug_tag = ''
+openstackdocs_repo_name = 'openstack/oslo.utils'
+openstackdocs_bug_project = 'oslo.utils'
+openstackdocs_bug_tag = ''
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']