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: If3aad2663d76fce58430d3b6ee6220ff550977a3
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

tox.ini

@@ -34,11 +34,13 @@ commands =
   stestr slowest
 
 [testenv:py35]
+basepython = python3
 commands =
   {[testenv]commands}
   stestr run '{posargs}'
 
 [testenv:docs]
+basepython = python3
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
   -r{toxinidir}/requirements.txt
@@ -46,6 +48,7 @@ deps =
 commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:cover]
+basepython = python3
 commands =
   coverage erase
   find . -type f -name "*.pyc" -delete
@@ -53,15 +56,18 @@ commands =
   coverage report
 
 [testenv:bandit]
+basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
 commands = bandit -r designate -n5 -x tests -t \
   B111,B505,B504,B503,B502,B501,B604,B605,B001,B601,B602,B701,B609,B702,\
   B608,B506,B312,B310,B411,B109,B108,B103,B102,B309,B308,B302,B307,B306
 
 [testenv:debug]
+basepython = python3
 commands = oslo_debug_helper -t designate/tests {posargs}
 
 [testenv:flake8]
+basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
 commands = sh tools/pretty_flake8.sh
   {[testenv:bandit]commands}
@@ -74,12 +80,15 @@ commands = sh tools/pretty_flake8.sh
   doc8 {posargs}
 
 [testenv:genconfig]
+basepython = python3
 commands = oslo-config-generator --config-file=etc/designate/designate-config-generator.conf
 
 [testenv:genpolicy]
+basepython = python3
 commands = oslopolicy-sample-generator --config-file etc/designate/designate-policy-generator.conf
 
 [testenv:bashate]
+basepython = python3
 deps = bashate
 whitelist_externals = bash
 commands = bash -c "find {toxinidir}/devstack         \
@@ -97,6 +106,7 @@ commands = bash -c "find {toxinidir}/devstack         \
          -print0 | xargs -0 bashate -v"
 
 [testenv:pip-check-reqs]
+basepython = python3
 # do not install test-requirements as that will pollute the virtualenv for
 # determining missing packages
 # this also means that pip-missing-reqs must be installed separately, outside
@@ -106,6 +116,7 @@ deps = pip-check-reqs
 commands=pip-missing-reqs -d --ignore-file=designate/tests/* designate
 
 [testenv:api-ref]
+basepython = python3
 # This environment is called from CI scripts to test and publish
 # the API Ref to developer.openstack.org.
 #
@@ -117,6 +128,7 @@ commands =
   sphinx-build -E -W -b html -d api-ref/build/doctrees api-ref/source api-ref/build/html
 
 [testenv:releasenotes]
+basepython = python3
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
   -r{toxinidir}/requirements.txt
@@ -124,6 +136,7 @@ deps =
 commands = sphinx-build -a -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [doc8]