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: I5f2ebf16d2768811f55939a55bedf59b808e0b9e
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

tox.ini

@@ -3,7 +3,6 @@ minversion = 2.0
 envlist = py35,py27,pep8
 
 [testenv]
-basepython = python3
 setenv =
     VIRTUAL_ENV={envdir}
     BRANCH_NAME=master
@@ -19,23 +18,28 @@ commands =
 basepython = python2.7
 
 [testenv:pep8]
+basepython = python3
 commands =
   flake8
   # Run security linter
   bandit -r oslo_log -x tests -n5
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:docs]
+basepython = python3
 commands = python setup.py build_sphinx
 
 [testenv:cover]
+basepython = python3
 commands =
   python setup.py test --coverage --coverage-package-name=oslo_log --testr-args='{posargs}'
   coverage report --show-missing
 
 [testenv:bandit]
+basepython = python3
 commands = bandit -r oslo_log -x tests -n5
 
 [flake8]
@@ -49,10 +53,12 @@ exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build,__init__.py
 import_exceptions = oslo_log._i18n
 
 [testenv:releasenotes]
+basepython = python3
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 
 [testenv:lower-constraints]
+basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt