Merge "fix tox python3 overrides"

tox.ini

@@ -12,6 +12,7 @@ commands = bash -c 'if [ ! -d ./.testrepository ] ; then testr init ; fi'
            testr run {posargs}
 
 [testenv:pep8]
+basepython = python3
 setenv =
     PYTHONPATH = .
 commands =
@@ -25,12 +26,14 @@ commands =
     check-uuid --fix --package heat_tempest_plugin
 
 [testenv:docs]
+basepython = python3
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
        sphinxcontrib-httpdomain
 commands = python setup.py build_sphinx
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [flake8]