Merge "fix tox python3 overrides"

tox.ini

@@ -72,9 +72,11 @@ commands =
   stestr run {posargs}
 
 [testenv:releasenotes]
+basepython = python3
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:pep8]
+basepython = python3
 commands =
   flake8
   pylint --rcfile=.pylintrc --output-format=colorized {posargs:neutron_vpnaas}
@@ -95,6 +97,7 @@ commands =
 commands = python ./tools/check_i18n.py ./neutron-vpnaas ./tools/i18n_cfg.py
 
 [testenv:cover]
+basepython = python3
 setenv =
     {[testenv]setenv}
     PYTHON=coverage run --source neutron_vpnaas --parallel-mode
@@ -106,9 +109,11 @@ commands =
   coverage xml -o cover/coverage.xml
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:docs]
+basepython = python3
 commands = sphinx-build -W -a -b html doc/source doc/build/html
 
 [flake8]