Use tox 3.1.1 fixes

By 3.1.1, tox had fixed:
- [1] which mishandled the basepython directive.
- ignoring PYTHONDONTWRITEBYTECODE [2]

Require this version and remove the workarounds.

See ML thread [3] for some details

[1] https://github.com/tox-dev/tox/issues/477
[2] 336f4f6bd8
[3] http://lists.openstack.org/pipermail/openstack-dev/2018-July/thread.html#132075

Change-Id: Iff442451c7a95caa7b9d22c76c341150175a34d1

tox.ini

@@ -1,7 +1,11 @@
 [tox]
-minversion = 2.1
+minversion = 3.1.1
 envlist = py{27,35},functional,pep8
 skipsdist = True
+# Automatic envs (pyXX) will use the python version appropriate to that
+# env and ignore basepython inherited from [testenv]. That's what we
+# want, and we don't need to be warned about it.
+ignore_basepython_conflict = True
 
 [testenv]
 basepython = python3
@@ -19,45 +23,31 @@ setenv =
   OS_STDOUT_CAPTURE=1
   OS_STDERR_CAPTURE=1
   OS_TEST_TIMEOUT=160
-  # NOTE(efried): This is only effective in tox versions after 3.0.0rc1
-  # https://github.com/tox-dev/tox/commit/336f4f6bd8b53223f940fc5cfc43b1bbd78d4699
   PYTHONDONTWRITEBYTECODE=1
 # TODO(stephenfin): Remove psycopg2 when minimum constraints is bumped to 2.8
   PYTHONWARNINGS = ignore::UserWarning:psycopg2
 deps = -r{toxinidir}/test-requirements.txt
-commands =
-  find . -type f -name "*.pyc" -delete
 passenv =
   OS_DEBUG GENERATE_HASHES
 # there is also secret magic in subunit-trace which lets you run in a fail only
 # mode. To do this define the TRACE_FAILONLY environmental variable.
 
 [testenv:py27]
-# TODO(efried): Remove this once https://github.com/tox-dev/tox/issues/425 is fixed.
-basepython = python2.7
 commands =
-  {[testenv]commands}
   stestr run {posargs}
   env TEST_OSPROFILER=1 stestr run --combine --no-discover 'nova.tests.unit.test_profiler'
   stestr slowest
 
 [testenv:py35]
-# TODO(efried): Remove this once https://github.com/tox-dev/tox/issues/425 is fixed.
-basepython = python3.5
 commands =
-  {[testenv]commands}
   stestr run {posargs}
   env TEST_OSPROFILER=1 stestr run --combine --no-discover 'nova.tests.unit.test_profiler'
 
 [testenv:py36]
-# TODO(efried): Remove this once https://github.com/tox-dev/tox/issues/425 is fixed.
-basepython = python3.6
 commands =
   {[testenv:py35]commands}
 
 [testenv:py37]
-# TODO(efried): Remove this once https://github.com/tox-dev/tox/issues/425 is fixed.
-basepython = python3.7
 commands =
   {[testenv:py35]commands}
 
@@ -100,7 +90,6 @@ deps =
   -r{toxinidir}/test-requirements.txt
   git+https://git.openstack.org/openstack/placement#egg=openstack-placement
 commands =
-  {[testenv]commands}
 # NOTE(cdent): The group_regex describes how stestr will group tests into the
 # same process when running concurently. The following ensures that gabbi tests
 # coming from the same YAML file are all in the same process. This is important
@@ -142,7 +131,6 @@ setenv =
   GENERATE_SAMPLES=True
   PYTHONHASHSEED=0
 commands =
-  {[testenv]commands}
   stestr --test-path=./nova/tests/functional/api_sample_tests run {posargs}
   stestr slowest
 
@@ -171,7 +159,6 @@ setenv =
   {[testenv]setenv}
   PYTHON=coverage run --source nova --parallel-mode
 commands =
-  {[testenv]commands}
   coverage erase
   stestr run {posargs}
   coverage combine
@@ -182,7 +169,6 @@ commands =
 [testenv:debug]
 envdir = {toxworkdir}/shared
 commands =
-  {[testenv]commands}
   oslo_debug_helper {posargs}
 
 [testenv:venv]
@@ -198,7 +184,6 @@ description =
   Build main documentation.
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
-  {[testenv]commands}
   rm -rf doc/build
   # Check that all JSON files don't have \r\n in line.
   bash -c "! find doc/ -type f -name *.json | xargs grep -U -n $'\r'"
@@ -214,7 +199,6 @@ description =
 envdir = {toxworkdir}/docs
 deps = {[testenv:docs]deps}
 commands =
-  {[testenv]commands}
   rm -rf api-guide/build
   sphinx-build -W -b html -d api-guide/build/doctrees api-guide/source api-guide/build/html
 
@@ -224,7 +208,6 @@ description =
 envdir = {toxworkdir}/docs
 deps = {[testenv:docs]deps}
 commands =
-  {[testenv]commands}
   rm -rf api-ref/build
   sphinx-build -W -b html -d api-ref/build/doctrees api-ref/source api-ref/build/html
 
@@ -234,7 +217,6 @@ description =
 envdir = {toxworkdir}/docs
 deps = {[testenv:docs]deps}
 commands =
-  {[testenv]commands}
   rm -rf releasenotes/build
   sphinx-build -W -b html -d releasenotes/build/doctrees releasenotes/source releasenotes/build/html
 
@@ -300,5 +282,4 @@ deps =
   -r{toxinidir}/test-requirements.txt
   -r{toxinidir}/requirements.txt
 commands =
-  {[testenv]commands}
   stestr run {posargs}