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: I27fd7e7310b2a1be3b283d43f40436ba5e165bbf

doc/source/conf.py

@@ -31,9 +31,10 @@ extensions = [
 
 
 # openstackdocstheme options
-repository_name = "openstack/keystone-specs"
-bug_project = "keystone"
-bug_tag = "specs"
+openstackdocs_repo_name = "openstack/keystone-specs"
+openstackdocs_auto_name = False
+openstackdocs_bug_project = "keystone"
+openstackdocs_bug_tag = "specs"
 
 blockdiag_html_image_format = 'SVG'
 
@@ -88,7 +89,7 @@ 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 = ['identity-specs.']

requirements.txt

@@ -2,9 +2,9 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 pbr>=2.0.0
-sphinx>=1.5.1,!=1.6.6,!=1.6.7,!=2.1.0  # BSD
+sphinx>=2.0.0,!=2.1.0 # BSD
 sphinxcontrib-blockdiag
-openstackdocstheme>=1.32.1 # Apache-2.0
+openstackdocstheme>=2.2.1 # Apache-2.0
 stestr>=2.0.0 # Apache-2.0
 testtools>=0.9.34
 doc8