Update docs building

Update docs building:
* Switch to sphinx-build
* Update requirements for Sphinx and openstackdocstheme for
  python 3
* Remove unneeded doc and translation sections from setup.cfg

Change-Id: Ie6cae5b1e7b600a2b2396f403a8fa5a90e5f3463
diff --git a/tox.ini b/tox.ini
index 19e006a..760cc47 100644
--- a/tox.ini
+++ b/tox.ini
@@ -13,8 +13,6 @@
    OS_LOG_CAPTURE={env:OS_LOG_CAPTURE:true}
    OS_STDOUT_CAPTURE={env:OS_STDOUT_CAPTURE:true}
    OS_STDERR_CAPTURE={env:OS_STDERR_CAPTURE:true}
-install_command =
-  pip install {opts} {packages}
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/test-requirements.txt
@@ -41,7 +39,7 @@
     coverage xml -o cover/coverage.xml
 
 [testenv:docs]
-commands = python setup.py build_sphinx
+commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:releasenotes]
 commands =