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: I9c427d9186e3e27b74d790839b1eb623769f57ec
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

tox.ini

@@ -31,9 +31,11 @@ commands =
   coverage report
 
 [testenv:debug]
+basepython = python3
 commands = oslo_debug_helper -t {env:OS_TEST_PATH} {posargs}
 
 [testenv:pep8]
+basepython = python3
 skip_install = True
 usedevelop = False
 commands =
@@ -42,28 +44,33 @@ commands =
   {[testenv:checkniceness]commands}
 
 [testenv:flake8]
+basepython = python3
 skip_install = True
 usedevelop = False
 commands = flake8 monascaclient
 
 [testenv:bandit]
+basepython = python3
 skip_install = True
 usedevelop = False
 commands = bandit -r monascaclient -n5 -x {env:OS_TEST_PATH}
 
 [testenv:docs]
+basepython = python3
 description = Builds full monascaclient documentation
 commands =
   {[testenv:devdocs]commands}
   {[testenv:releasenotes]commands}
 
 [testenv:devdocs]
+basepython = python3
 description = Builds developer documentation
 commands =
   rm -rf {toxinidir}/doc/build {toxinidir}/doc/source/contributor/api
   python setup.py build_sphinx
 
 [testenv:releasenotes]
+basepython = python3
 description = Called from CI script to test and publish the Release Notes
 commands =
   rm -rf releasenotes/build
@@ -71,12 +78,14 @@ commands =
     {toxinidir}/releasenotes/source {toxinidir}/releasenotes/build/html
 
 [testenv:checkniceness]
+basepython = python3
 description = Validates (pep-like) documenation
 commands =
   doc8 --file-encoding utf-8 {toxinidir}/doc
   doc8 --file-encoding utf-8 {toxinidir}/releasenotes
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [hacking]