Merge "fix tox python3 overrides"

tox.ini

@@ -13,9 +13,11 @@ deps = -r{toxinidir}/requirements.txt
 commands = stestr run --slowest {posargs}
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:docs]
+basepython = python3
 commands = python setup.py build_sphinx
 
 [testenv:spelling]
@@ -26,6 +28,7 @@ deps =
 commands = sphinx-build -b spelling doc/source doc/build/spelling
 
 [testenv:cover]
+basepython = python3
 setenv =
     PYTHON=coverage run --source specs --parallel-mode
 commands =
@@ -35,6 +38,7 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:pep8]
+basepython = python3
 commands = flake8
 
 [flake8]