Drop redundant injection of VIRTUAL_ENV

tox automatically injects the environment so no manual override is
necessary.

Also remove basepython because tox uses the python version where tox
is installed by default, and we no longer expect that the tests may run
in env with python 2.

Change-Id: I95f32db44f04658843ad6b09bed2505a90a53507

tox.ini

@@ -1,41 +1,37 @@
 [tox]
 minversion = 3.2.0
 envlist = py3,pep8
-ignore_basepython_conflict = True
 
 [testenv]
-basepython = python3
-setenv =
-    VIRTUAL_ENV={envdir}
 deps =
  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
  -r{toxinidir}/test-requirements.txt
  -r{toxinidir}/requirements.txt
 commands =
-    stestr run --slowest {posargs}
+  stestr run --slowest {posargs}
 
 [testenv:debug]
 commands = oslo_debug_helper {posargs}
 
 [testenv:pep8]
 deps =
-    pre-commit>=2.6.0 # MIT
-    {[testenv:docs]deps}
+  pre-commit>=2.6.0 # MIT
+  {[testenv:docs]deps}
 commands =
-    pre-commit run -a
-    sphinx-build -b doctest doc/source doc/build
+  pre-commit run -a
+  sphinx-build -b doctest doc/source doc/build
 
 [testenv:venv]
 commands = {posargs}
 
 [testenv:cover]
 setenv =
-    PYTHON=coverage run --source $project --parallel-mode
+  PYTHON=coverage run --source $project --parallel-mode
 commands =
-    stestr run {posargs}
-    coverage combine
-    coverage html -d cover
-    coverage xml -o cover/coverage.xml
+  stestr run {posargs}
+  coverage combine
+  coverage html -d cover
+  coverage xml -o cover/coverage.xml
 
 [testenv:docs]
 deps =