Cleanup py27 support

This repo is now testing only with Python 3, so let's make
a few cleanups:
- Remove obsolete sections from setup.cfg
- Remove install_command from tox.ini, the default is fine
- Use python3 everywhere in tox.ini

Change-Id: I2ff47a5a7b9d44f99e2fbd5fc5208ab9f53c69fa

setup.cfg

@@ -12,13 +12,3 @@ classifier =
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
 
-[build_sphinx]
-source-dir = doc/source
-build-dir = doc/build
-all_files = 1
-
-[pbr]
-warnerrors = True
-
-[upload_sphinx]
-upload-dir = doc/build/html

tox.ini

@@ -1,26 +1,23 @@
 [tox]
-minversion = 1.6
+minversion = 3.2.0
 envlist = docs
 skipsdist = True
 
 [testenv]
+basepython = python3
 usedevelop = True
-install_command = pip install -U {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:docs]
-basepython = python3
 commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:spelling]
-basepython = python3
 deps =
    -r{toxinidir}/requirements.txt
    sphinxcontrib-spelling