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/tox.ini b/tox.ini
index f42a5b5..c598d9e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,7 +7,6 @@
 [testenv]
 basepython = python3
 usedevelop = True
-install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
    OS_TEST_PATH=./patrole_tempest_plugin/tests/unit
@@ -16,8 +15,10 @@
    PYTHONWARNINGS=default::DeprecationWarning
 passenv = OS_STDOUT_CAPTURE OS_STDERR_CAPTURE OS_TEST_TIMEOUT OS_TEST_LOCK_PATH http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 whitelist_externals = find
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+deps =
+    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+    -r{toxinidir}/requirements.txt
+    -r{toxinidir}/test-requirements.txt
 commands =
     find . -type f -name "*.pyc" -delete
     stestr --test-path ./patrole_tempest_plugin/tests/unit run {posargs}
@@ -70,10 +71,7 @@
    make -C doc/build/pdf
 
 [testenv:releasenotes]
-deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
-  -r{toxinidir}/requirements.txt
-  -r{toxinidir}/doc/requirements.txt
+deps = {[testenv:docs]deps}
 commands =
   rm -rf releasenotes/build
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html