Trivial cleanup for tox

move 'basepython' to the top-level 'testenv'

Change-Id: I197d6486a3b126f616ffe2f7e3e669d922a1e337

tox.ini

@@ -1,9 +1,10 @@
 [tox]
-minversion = 2.5.0
+minversion = 3.1
 envlist = py27,py37,pep8,docs
+ignore_basepython_conflict = True
 
 [testenv]
-install_command = pip install {opts} {packages}
+basepython = python3
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
   -r{toxinidir}/test-requirements.txt
@@ -13,7 +14,6 @@ commands =
   stestr slowest
 
 [testenv:pep8]
-basepython = python3
 deps =
   -r{toxinidir}/test-requirements.txt
 commands =
@@ -22,7 +22,6 @@ commands =
   bandit -r oslo_limit tests -n5
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:docs]
@@ -30,18 +29,15 @@ deps =
   -r{toxinidir}/test-requirements.txt
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/doc/requirements.txt
-basepython = python3
 whitelist_externals = rm
 commands =
   rm -fr doc/build
   sphinx-build -W --keep-going -b html doc/source doc/build/html
 
 [testenv:cover]
-basepython = python3
 commands = python setup.py test --coverage --coverage-package-name=oslo_limit --testr-args='{posargs}'
 
 [testenv:releasenotes]
-basepython = python3
 whitelist_externals = rm
 deps =
   -r{toxinidir}/doc/requirements.txt
@@ -59,7 +55,6 @@ exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build
 import_exceptions = oslo_limit._i18n
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt