Switch to newer openstackdocstheme and reno versions

Switch to openstackdocstheme 2.2.1 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.

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: If9a4d4ca32793fef56b3e5c9a6508f7383476558

doc/requirements.txt

@@ -1,6 +1,6 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-openstackdocstheme>=1.18.1 # Apache-2.0
-reno>=2.5.0 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,>=1.6.2  # BSD
+openstackdocstheme>=2.2.1 # Apache-2.0
+reno>=3.1.0 # Apache-2.0
+sphinx>=2.0.0,!=2.1.0 # BSD

doc/source/conf.py

@@ -27,9 +27,10 @@ extensions = [
 ]
 
 # openstackdocstheme options
-repository_name = 'openstack/os-testr'
-bug_project = 'os-testr'
-bug_tag = ''
+openstackdocs_repo_name = 'openstack/os-testr'
+openstackdocs_auto_name = False
+openstackdocs_bug_project = 'os-testr'
+openstackdocs_bug_tag = ''
 
 # autodoc generation is a bit aggressive and a nuisance when doing heavy
 # text edit cycles.
@@ -53,7 +54,7 @@ add_function_parentheses = True
 add_module_names = True
 
 # The name of the Pygments (syntax highlighting) style to use.
-pygments_style = 'sphinx'
+pygments_style = 'native'
 
 # -- Options for HTML output --------------------------------------------------
 

releasenotes/source/conf.py

@@ -46,12 +46,10 @@ extensions = [
 ]
 
 # openstackdocstheme options
-repository_name = 'openstack/os-testr'
-bug_project = 'os-testr'
-bug_tag = ''
-
-# Must set this variable to include year, month, day, hours, and minutes.
-html_last_updated_fmt = '%Y-%m-%d %H:%M'
+openstackdocs_repo_name = 'openstack/os-testr'
+openstackdocs_auto_name = False
+openstackdocs_bug_project = 'os-testr'
+openstackdocs_bug_tag = ''
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
@@ -78,7 +76,7 @@ version = ''
 exclude_patterns = []
 
 # The name of the Pygments (syntax highlighting) style to use.
-pygments_style = 'sphinx'
+pygments_style = 'native'
 
 # -- Options for HTML output -------------------------------------------------