Ensure python versions

It looks like better to specify basepython for all tox envs.
As of the queens release, we use python 2.7 by default.

http://lists.openstack.org/pipermail/openstack-discuss/2019-November/010957.html

Change-Id: I586d1f63039b71f2ec757b06eb32a30a52705568

tox.ini

@@ -32,21 +32,25 @@ setenv =
 commands = {[unit_tests]commands}
 
 [testenv:py27dj18]
+basepython = python2.7
 commands =
   pip install -U django>=1.8,<1.9
   {[unit_tests]commands}
 
 [testenv:py27dj19]
+basepython = python2.7
 commands =
   pip install -U django>=1.9,<1.10
   {[unit_tests]commands}
 
 [testenv:py27dj110]
+basepython = python2.7
 commands =
   pip install -U django>=1.10,<1.11
   {[unit_tests]commands}
 
 [testenv:py27dj111]
+basepython = python2.7
 commands =
   pip install -U django>=1.11,<2.0
   {[unit_tests]commands}
@@ -65,6 +69,7 @@ commands =
     bash {toxinidir}/tools/unit_tests.sh {envpython} {toxinidir} {posargs}
 
 [testenv:pep8]
+basepython = python2.7
 commands =
   flake8 {posargs}
   {envpython} {toxinidir}/manage.py extract_messages --verbosity 0 --check-only
@@ -72,6 +77,7 @@ commands =
   doc8 doc/source releasenotes/source releasenotes/notes
 
 [testenv:cover]
+basepython = python2.7
 commands =
   coverage erase
   coverage run {toxinidir}/manage.py test horizon --settings=horizon.test.settings {posargs}
@@ -81,6 +87,7 @@ commands =
   coverage html
 
 [testenv:selenium]
+basepython = python2.7
 setenv =
   {[testenv]setenv}
   WITH_SELENIUM=1
@@ -88,6 +95,7 @@ setenv =
 commands = {[unit_tests]commands}
 
 [testenv:selenium-headless]
+basepython = python2.7
 setenv =
   {[testenv]setenv}
   SELENIUM_HEADLESS=1
@@ -96,6 +104,7 @@ setenv =
 commands = {[unit_tests]commands}
 
 [testenv:selenium-phantomjs]
+basepython = python2.7
 setenv =
   {[testenv]setenv}
   SELENIUM_PHANTOMJS=1
@@ -104,6 +113,7 @@ setenv =
 commands = {[unit_tests]commands}
 
 [testenv:py27integration]
+basepython = python2.7
 # Run integration tests only
 passenv = AVCONV_INSTALLED
 setenv =
@@ -112,10 +122,10 @@ setenv =
   SELENIUM_HEADLESS=1
   NOSE_WITH_OPENSTACK=1
   NOSE_OPENSTACK_SHOW_ELAPSED=1
-basepython = python2.7
 commands = nosetests openstack_dashboard.test.integration_tests {posargs}
 
 [testenv:npm]
+basepython = python2.7
 passenv =
   HOME
   DISPLAY
@@ -125,6 +135,7 @@ commands =
   npm run {posargs:test}
 
 [testenv:tests_system_packages]
+basepython = python2.7
 # Provide an environment for system packagers that dont want anything from pip
 # Any extra deps needed for this env can be passed by setting TOX_EXTRA_DEPS
 sitepackages = True
@@ -136,16 +147,19 @@ commands =
   {[unit_tests]commands}
 
 [testenv:docs]
+basepython = python2.7
 commands =
   doc8 doc/source
   sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:releasenotes]
+basepython = python2.7
 commands =
   doc8 releasenotes/source releasenotes/notes
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:manage]
+basepython = python2.7
 # we don't need to install test-requirements.txt
 # modules in requirements.txt are installed due to usedevelop=True
 # so 'deps' can be empty.