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: I31a207868c07e08ae27c14635d52506021032cb7
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

tox.ini

@@ -3,7 +3,6 @@ minversion = 2.0
 envlist = py35,py27,pep8
 
 [testenv]
-basepython = python3
 install_command = pip install {opts} {packages}
 whitelist_externals = bash
                       env
@@ -26,6 +25,7 @@ commands =
 passenv = OS_TEST_DBAPI_ADMIN_CONNECTION
 
 [testenv:sqla_09]
+basepython = python3
 commands = pip install SQLAlchemy>=0.9.0,!=0.9.5,<1.0.0
             python setup.py testr --slowest --testr-args='{posargs}'
 
@@ -36,24 +36,29 @@ commands =
     env TEST_EVENTLET=1 bash tools/pretty_tox.sh '{posargs}'
 
 [testenv:pep8]
+basepython = python3
 commands =
   flake8
   # Run security linter
   bandit -r oslo_db -x tests -n5 --skip B105,B311
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:cover]
+basepython = python3
 commands = python setup.py test --coverage --coverage-package-name=oslo_db --testr-args='{posargs}'
 
 [testenv:docs]
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
     doc8 -e .rst CONTRIBUTING.rst HACKING.rst README.rst doc/source
     sphinx-build -b html doc/source doc/build/html
 
 [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
 
@@ -68,6 +73,7 @@ import_exceptions =
   oslo_db._i18n
 
 [testenv:lower-constraints]
+basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt