Cleanup py27 support

This repo is now testing only with Python 3, so let's make
a few cleanups:
- Remove python 2.7 stanza from setup.py
- Remove obsolete sections from setup.cfg
- Update classifiers
- Use newer openstackdocstheme and Sphinx versions
- Cleanup */source/conf.py to remove now obsolete content.
- Remove install_command from tox.ini, the default is fine
- Remove hacking requirements from lower-constraints, they
  are not needed for install

Change-Id: I150a5ee2cd08abf5ce9cf9daf2835007dea0dffd
diff --git a/setup.cfg b/setup.cfg
index f8f0257..b99f7f2 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -14,6 +14,8 @@
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     Programming Language :: Python
+    Programming Language :: Python :: Implementation :: CPython
+    Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
@@ -22,14 +24,6 @@
 packages =
     patrole_tempest_plugin
 
-[upload_sphinx]
-upload-dir = doc/build/html
-
-[build_releasenotes]
-all_files = 1
-build-dir = releasenotes/build
-source-dir = releasenotes/source
-
 [entry_points]
 tempest.test_plugins =
     patrole_tests = patrole_tempest_plugin.plugin:PatroleTempestPlugin