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: Ifc418b2911ec09d1f7968ffb3d3e4093f6d07d6c
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

tox.ini

@@ -18,19 +18,23 @@ whitelist_externals =
   find
 
 [testenv:pep8]
+basepython = python3
 commands = flake8 {posargs}
 
 [testenv:genconfig]
+basepython = python3
 commands =
     oslo-config-generator --config-file tools/config/config-generator.qinling.conf \
     --output-file etc/qinling.conf.sample
 
 #set PYTHONHASHSEED=0 to prevent oslo_policy.sphinxext from randomly failing.
 [testenv:venv]
+basepython = python3
 setenv = PYTHONHASHSEED=0
 commands = {posargs}
 
 [testenv:cover]
+basepython = python3
 setenv =
     {[testenv]setenv}
     PYTHON=coverage run --source qinling --parallel-mode
@@ -38,6 +42,7 @@ commands =
     {toxinidir}/tools/cover.sh {posargs}
 
 [testenv:docs]
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 whitelist_externals = rm
 commands =
@@ -45,11 +50,13 @@ commands =
   sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:releasenotes]
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:debug]
+basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [flake8]