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.

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: I61c96d3f8479b6ab5eef993a769f1fc7df78c6ad

doc/requirements.txt

@@ -2,11 +2,11 @@
 # with g-r on purpose, as g-r is just for projects affecting the
 # integrated gate. Any sync must happen manually as recommended by
 # the openstack release team.
-sphinx>=1.6.2 # BSD
+sphinx>=2.0.0,!=2.1.0 # BSD
 actdiag
 blockdiag
 nwdiag
-openstackdocstheme>=1.32.1 # Apache-2.0
+openstackdocstheme>=2.2.1 # Apache-2.0
 seqdiag
 sphinxcontrib-actdiag
 sphinxcontrib-blockdiag # BSD

doc/source/conf.py

@@ -37,12 +37,12 @@ extensions = [
              ]
 
 # config for openstackdocstheme
-repository_name = 'openstack/neutron-specs'
-bug_project = 'neutron'
-bug_tag = ''
+openstackdocs_repo_name = 'openstack/neutron-specs'
+openstackdocs_bug_project = 'neutron'
+openstackdocs_bug_tag = ''
 
 # Feed configuration for yasfb
-feed_base_url = 'http://specs.openstack.org/openstack/neutron-specs'
+feed_base_url = 'https://specs.openstack.org/openstack/neutron-specs'
 feed_author = 'OpenStack Neutron Team'
 
 todo_include_todos = True
@@ -97,7 +97,7 @@ 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 = ['neutron-specs.']