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: I0db7cdc38ed8392ec4358467115b6d715c71bb29
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

tox.ini

@@ -19,6 +19,7 @@ commands =
 whitelist_externals = rm
 
 [testenv:cover]
+basepython = python3
 deps =
     {[testenv]deps}
     diff_cover
@@ -29,11 +30,13 @@ commands =
     diff-cover --fail-under 100 --compare-branch master coverage.xml
 
 [testenv:releasenotes]
+basepython = python3
 commands =
   rm -rf releasenotes/build
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:pep8]
+basepython = python3
 sitepackages = False
 commands =
   flake8 {posargs}
@@ -41,15 +44,18 @@ commands =
   bandit -r barbican -x tests -n5
 
 [testenv:genconfig]
+basepython = python3
 whitelist_externals = bash
 envdir = {toxworkdir}/pep8
 commands =
   oslo-config-generator --config-file etc/oslo-config-generator/barbican.conf
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:debug]
+basepython = python3
 commands = oslo_debug_helper -t barbican/tests {posargs}
 
 [testenv:py3pep8]
@@ -62,6 +68,7 @@ commands =
   flake8 barbican setup.py
 
 [testenv:docs]
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands=
     rm -rf doc/build api-guide/build api-ref/build
@@ -71,6 +78,7 @@ commands=
 whitelist_externals = rm
 
 [testenv:api-guide]
+basepython = python3
 # This environment is called from CI scripts to test and publish
 # the API Guide to developer.openstack.org.
 commands =
@@ -78,6 +86,7 @@ commands =
   sphinx-build -W -b html -d api-guide/build/doctrees api-guide/source api-guide/build/html
 
 [testenv:api-ref]
+basepython = python3
 # This environment is called from CI scripts to test and publish
 # the API Ref to developer.openstack.org.
 commands =
@@ -104,6 +113,7 @@ commands =
 passenv = KMIP_PLUGIN_ENABLED
 
 [testenv:cmd]
+basepython = python3
 # This tox env is purely to make local test development easier
 # Note: This requires local running instances of Barbican and Keystone
 deps = -r{toxinidir}/test-requirements.txt
@@ -118,10 +128,12 @@ exclude = .git,.idea,.tox,bin,dist,debian,rpmbuild,tools,*.egg-info,*.eggs,contr
           *docs/target,*.egg,build
 
 [testenv:bandit]
+basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
 commands = bandit -r barbican -x tests -n5
 
 [testenv:bindep]
+basepython = python3
 # Do not install any requirements. We want this to be fast and work even if
 # system dependencies are missing, since it's used to tell you what system
 # dependencies are missing! This also means that bindep must be installed
@@ -130,6 +142,7 @@ deps = bindep
 commands = bindep test
 
 [testenv:genpolicy]
+basepython = python3
 envdir = {toxworkdir}/pep8
 commands = oslopolicy-sample-generator --config-file=etc/oslo-config-generator/policy.conf