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: I02ef155ef47a5eaddf9de902ad3608bee677fbcf
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

tox.ini

@@ -3,7 +3,6 @@ minversion = 2.0
 envlist = py35,py27,pep8,bandit
 
 [testenv]
-basepython = python3
 setenv =
     VIRTUAL_ENV={envdir}
 passenv = OS_*
@@ -16,22 +15,22 @@ deps =
   -r{toxinidir}/requirements.txt
 commands = python setup.py testr --slowest --testr-args='{posargs}'
 
-[testenv:py27]
-basepython = python2.7
-
 [testenv:pep8]
+basepython = python3
 commands = flake8
 deps = hacking<0.11,>=0.10.0
 
 [testenv:cover]
+basepython = python3
 commands =
   python setup.py test --coverage --coverage-package-name=oslo_messaging --testr-args='{posargs}'
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:docs]
-basepython = python2.7
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -W -b html doc/source doc/build/html
 
@@ -43,6 +42,7 @@ setenv =
 commands = pifpaf run rabbitmq --  python setup.py testr --slowest --testr-args='{posargs:oslo_messaging.tests.functional}'
 
 [testenv:py35-func-rabbit]
+basepython = python3.5
 setenv =
     {[testenv]setenv}
     TRANSPORT_DRIVER=rabbit
@@ -67,6 +67,7 @@ setenv =
 commands = {toxinidir}/tools/setup-test-env-amqp1.sh python setup.py testr --slowest --testr-args='{posargs:oslo_messaging.tests.functional}'
 
 [testenv:py35-func-amqp1]
+basepython = python3.5
 setenv =
     {[testenv]setenv}
     TRANSPORT_URL=amqp://stackqpid:secretqpid@127.0.0.1:65123//
@@ -76,6 +77,7 @@ setenv =
 commands = {toxinidir}/tools/setup-test-env-amqp1.sh python setup.py testr --slowest --testr-args='{posargs:oslo_messaging.tests.functional}'
 
 [testenv:py35-func-kafka]
+basepython = python3.5
 setenv =
     {[testenv]setenv}
     TRANSPORT_URL=kafka://127.0.0.1:9092/
@@ -87,6 +89,7 @@ basepython = python2.7
 commands = {toxinidir}/setup-test-env-zmq.sh python setup.py testr --slowest --testr-args='{posargs:oslo_messaging.tests.functional}'
 
 [testenv:py35-func-zmq]
+basepython = python3.5
 commands = {toxinidir}/setup-test-env-zmq.sh python setup.py testr --slowest --testr-args='{posargs:oslo_messaging.tests.functional}'
 
 [testenv:py27-func-zmq-dyn]
@@ -102,6 +105,7 @@ basepython = python2.7
 commands = {toxinidir}/setup-test-env-zmq-pub-sub.sh python setup.py testr --slowest --testr-args='{posargs:oslo_messaging.tests.functional}'
 
 [testenv:bandit]
+basepython = python3
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
   -r{toxinidir}/test-requirements.txt
@@ -121,14 +125,17 @@ import_exceptions =
 local-check-factory = oslo_messaging.hacking.checks.factory
 
 [testenv:releasenotes]
+basepython = python3
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 deps = -r{toxinidir}/doc/requirements.txt
 
 [testenv:bindep]
+basepython = python3
 deps = bindep
 commands = bindep {posargs}
 
 [testenv:lower-constraints]
+basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt