fix tox python3 overrides

We want to default to running all tox environments under python 3, so
set the basepython value in each environment.

We do not want to specify a minor version number, because we do not
want to have to update the file every time we upgrade python.

We do not want to set the override once in testenv, because that
breaks the more specific versions used in default environments like
py35 and py36.

Change-Id: Ic87686868f784f0e1b514d6b899cc16240d88d61

tox.ini

@@ -16,12 +16,15 @@ setenv =
 passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:releasenotes]
+basepython = python3
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:cover]
+basepython = python3
 setenv =
     {[testenv]setenv}
     PYTHON=coverage run --branch --omit='*test*' --source ironic_inspector --parallel-mode
@@ -33,7 +36,7 @@ commands =
     coverage html -d ./cover --omit='*test*'
 
 [testenv:pep8]
-basepython = python2.7
+basepython = python3
 commands =
     flake8 ironic_inspector
     doc8 README.rst CONTRIBUTING.rst doc/source
@@ -49,15 +52,18 @@ commands =
     python3 -m ironic_inspector.test.functional
 
 [testenv:genconfig]
+basepython = python3
 envdir = {toxworkdir}/venv
 commands = oslo-config-generator --config-file config-generator.conf
 
 [testenv:genpolicy]
+basepython = python3
 sitepackages = False
 envdir = {toxworkdir}/venv
 commands = oslopolicy-sample-generator --config-file {toxinidir}/policy-generator.conf
 
 [testenv:genstates]
+basepython = python3
 deps = {[testenv]deps}
 commands = {toxinidir}/tools/states_to_dot.py -f {toxinidir}/doc/source/images/states.svg --format svg
 
@@ -78,6 +84,7 @@ application-import-names = ironic_inspector
 import_exceptions = ironicclient.exceptions,ironic_inspector.common.i18n
 
 [testenv:docs]
+basepython = python3
 setenv = PYTHONHASHSEED=0
 sitepackages = False
 deps = -r{toxinidir}/test-requirements.txt