Merge "fix tox python3 overrides"

tox.ini

@@ -28,14 +28,17 @@ setenv =
    DJANGO_SETTINGS_MODULE=monitoring.test.settings
 
 [testenv:pep8]
+basepython = python3
 commands =
   /bin/bash run_tests.sh -N --pep8
   python setup.py check --restructuredtext --strict
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:cover]
+basepython = python3
 commands = /bin/bash run_tests.sh -N --coverage {posargs}
 
 [flake8]
@@ -44,6 +47,7 @@ builtins = _
 exclude = .venv,.git,.tox,dist,*lib/python*,*egg,build,panel_template,dash_template,local_settings.py,*/local/*,*/test/test_plugins/*
 
 [testenv:lower-constraints]
+basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt