Switch to newer openstackdocstheme version

Switch to openstackdocstheme 2.2.1 version. Using
this version will allow especially:
* Linking from HTML to PDF document
* Allow parallel building of documents
* Fix some rendering problems

Update Sphinx version as well.

Disable openstackdocs_auto_name to use 'project' variable as name.

Change pygments_style to 'native' since old theme version always used
'native' and the theme now respects the setting and using 'sphinx' can
lead to some strange rendering.

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.

See also
http://lists.openstack.org/pipermail/openstack-discuss/2020-May/014971.html

Change-Id: If046b8dded45c939bf596fdc8ae95f0d34602054

doc/source/conf.py

@@ -10,10 +10,6 @@
 # serve to show the default.
 
 import datetime
-import subprocess
-import sys
-import os
-import warnings
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
@@ -35,7 +31,7 @@ extensions = [
              ]
 
 # Feed configuration for yasfb
-feed_base_url = 'http://specs.openstack.org/openstack/mistral-specs'
+feed_base_url = 'https://specs.openstack.org/openstack/mistral-specs'
 feed_author = 'OpenStack Mistral Team'
 
 todo_include_todos = True
@@ -47,9 +43,10 @@ templates_path = ['_templates']
 source_suffix = '.rst'
 
 html_theme = 'openstackdocs'
-repository_name = 'openstack/mistral-specs'
-bug_project = 'mistral'
-bug_tag = 'specs'
+openstackdocs_repo_name = 'openstack/mistral-specs'
+openstackdocs_auto_name = False
+openstackdocs_bug_project = 'mistral'
+openstackdocs_bug_tag = 'specs'
 
 
 # The encoding of source files.
@@ -95,7 +92,7 @@ add_module_names = False
 show_authors = False
 
 # The name of the Pygments (syntax highlighting) style to use.
-pygments_style = 'sphinx'
+pygments_style = 'native'
 
 # A list of ignored prefixes for module index sorting.
 modindex_common_prefix = ['mistral-specs.']

requirements.txt

@@ -1,5 +1,5 @@
 pbr>=2.0,!=2.1.0  # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,!=2.1.0,>=1.6.2 # BSD
-openstackdocstheme>=1.32.0 # Apache-2.0
+sphinx>=2.0.0,!=2.1.0 # BSD
+openstackdocstheme>=2.2.1 # Apache-2.0
 testtools>=0.9.34
 yasfb