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: Ib3db49d1256072975e9f3a9472cb27ca6d9895f6

doc/source/conf.py

@@ -30,8 +30,9 @@
 extensions = ['openstackdocstheme']
 
 # Settings for openstackdocstheme
-repository_name = 'openstack/adjutant-ui'
-use_storyboard = True
+openstackdocs_repo_name = 'openstack/adjutant-ui'
+openstackdocs_auto_name = False
+openstackdocs_use_storyboard = True
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
@@ -55,7 +56,7 @@ copyright = u'2017, Catalyst IT Ltd'
 exclude_patterns = []
 
 # The name of the Pygments (syntax highlighting) style to use.
-pygments_style = 'sphinx'
+pygments_style = 'native'
 
 # If true, `todo` and `todoList` produce output, else they produce nothing.
 todo_include_todos = False

lower-constraints.txt

@@ -45,7 +45,7 @@ munch==2.5.0
 netaddr==0.7.19
 netifaces==0.10.9
 nodeenv==0.9.4
-openstackdocstheme==2.0.0
+openstackdocstheme==2.2.1
 openstacksdk==0.43.0
 os-client-config==2.0.0
 os-service-types==1.7.0
@@ -82,7 +82,7 @@ python-swiftclient==3.9.0
 pytz==2019.3
 PyYAML==5.3.1
 rcssmin==1.0.6
-reno==2.5.0
+reno==3.1.0
 requests==2.23.0
 requestsexceptions==1.4.0
 rfc3986==1.3.2

test-requirements.txt

@@ -10,10 +10,10 @@
 hacking>=3.0,<3.1 # Apache-2.0
 coverage>=4.0 # Apache-2.0
 nodeenv>=0.9.4 # BSD
-reno>=2.5.0 # Apache-2.0
+reno>=3.1.0 # Apache-2.0
 selenium>=2.50.1 # Apache-2.0
-sphinx!=2.1.0,>=2.0.0 # BSD
+sphinx>=2.0.0,!=2.1.0 # BSD
 testtools>=1.4.0 # MIT
 # This also needs xvfb library installed on your OS
 xvfbwrapper>=0.1.3 #license: MIT
-openstackdocstheme>=2.0.0 # Apache-2.0
+openstackdocstheme>=2.2.1 # Apache-2.0