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: I6f1df527590d7b9ffdf7dd97c0fedf27f11b9e21
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

tox.ini

@@ -19,6 +19,7 @@ commands =
 whitelist_externals = bash
 
 [testenv:integration]
+basepython = python3
 setenv = OS_TEST_PATH=./ceilometer/tests/integration
          OS_TEST_TIMEOUT=2400
          GABBI_LIVE_FAIL_IF_NO_TEST=1
@@ -29,11 +30,13 @@ commands =
    bash -c 'cd ceilometer/tests/integration/gabbi/gabbits-live && gabbi-run -x < autoscaling.yaml'
 
 [testenv:cover]
+basepython = python3
 setenv = OS_TEST_PATH=ceilometer/tests
 commands =
    python setup.py testr --slowest --coverage --testr-args="{posargs}"
 
 [testenv:pep8]
+basepython = python3
 deps = hacking<0.13,>=0.12
        doc8
 commands =
@@ -43,16 +46,20 @@ commands =
     bash -c "find ceilometer -type f -regex '.*\.pot?' -print0|xargs -0 -n 1 msgfmt --check-format -o /dev/null"
 
 [testenv:releasenotes]
+basepython = python3
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:genconfig]
+basepython = python3
 commands = oslo-config-generator --config-file=etc/ceilometer/ceilometer-config-generator.conf
 
 [testenv:docs]
+basepython = python3
 commands = python setup.py build_sphinx
 setenv = PYTHONHASHSEED=0
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 setenv = PYTHONHASHSEED=0