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: I0c58db720967236b55e1aa084059c994548d5307
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

tox.ini

@@ -24,6 +24,7 @@ commands =
 passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 
 [testenv:pep8]
+basepython = python3
 commands =
   doc8 -e .rst doc/source/ CONTRIBUTING.rst HACKING.rst README.rst
   bash tools/flake8wrap.sh {posargs}
@@ -33,11 +34,13 @@ commands =
   bandit -r zun -x tests -n5 -ll --skip B303,B604
 
 [testenv:venv]
+basepython = python3
 #set PYTHONHASHSEED=0 to prevent oslo_policy.sphinxext from randomly failing.
 setenv = PYTHONHASHSEED=0
 commands = {posargs}
 
 [testenv:cover]
+basepython = python3
 setenv =
     {[testenv]setenv}
     PYTHON=coverage run --source zun --parallel-mode
@@ -49,12 +52,14 @@ commands =
     coverage report
 
 [testenv:docs]
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
     doc8 -e .rst specs/ doc/source/ CONTRIBUTING.rst HACKING.rst README.rst
     sphinx-build -W -d doc/build/doctrees -b html doc/source/ doc/build/html
 
 [testenv:debug]
+basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [testenv:debug-py27]
@@ -66,6 +71,7 @@ basepython = python3.5
 commands = oslo_debug_helper {posargs}
 
 [testenv:migration]
+basepython = python3
 setenv = {[testenv]setenv}
    OS_TEST_PATH=./zun/tests/migration
 deps = {[testenv]deps}
@@ -87,6 +93,7 @@ exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build
 local-check-factory = zun.hacking.checks.factory
 
 [testenv:fast8]
+basepython = python3
 # NOTE(sheel.rana): `tox -e fast8` cab be used to run pep8 command only for
 # updated code instead for running whole code base.
 # Use same environment directory as pep8 env to save space and install time.
@@ -96,19 +103,23 @@ commands =
   {toxinidir}/tools/fast8.sh
 
 [testenv:releasenotes]
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:genconfig]
+basepython = python3
 envdir = {toxworkdir}/venv
 commands =
     oslo-config-generator --config-file etc/zun/zun-config-generator.conf
 
 [testenv:genpolicy]
+basepython = python3
 commands =
     oslopolicy-sample-generator --config-file etc/zun/zun-policy-generator.conf
 
 [testenv:api-ref]
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
   rm -rf api-ref/build