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: I9dc0c5d49b29557435f7b356fe3aaa5554849d93

tox.ini

@@ -1,13 +1,10 @@
 [tox]
-minversion = 3.18.0
+minversion = 4.0.0
 envlist = py3,pep8
-ignore_basepython_conflict = True
 
 [testenv]
 usedevelop = True
-basepython = python3
 setenv =
-  VIRTUAL_ENV={envdir}
   OS_TEST_PATH=./castellan/tests/unit
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
@@ -30,14 +27,14 @@ commands = oslo_debug_helper {posargs}
 
 [testenv:cover]
 setenv =
-    PYTHON=coverage run --source castellan --parallel-mode
+  PYTHON=coverage run --source castellan --parallel-mode
 commands =
-    coverage erase
-    {[testenv]commands}
-    coverage combine
-    coverage html -d cover
-    coverage xml -o cover/coverage.xml
-    coverage report --show-missing
+  coverage erase
+  {[testenv]commands}
+  coverage combine
+  coverage html -d cover
+  coverage xml -o cover/coverage.xml
+  coverage report --show-missing
 
 [testenv:docs]
 # This environment is called from CI scripts to test and publish
@@ -68,25 +65,23 @@ commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasen
 [testenv:functional]
 usedevelop = True
 setenv =
-    VIRTUAL_ENV={envdir}
-    OS_TEST_PATH=./castellan/tests/functional
+  OS_TEST_PATH=./castellan/tests/functional
 commands = stestr run --slowest --concurrency=1 {posargs}
 
 [testenv:functional-vault]
 passenv = HOME
 usedevelop = True
 setenv =
-    VIRTUAL_ENV={envdir}
-    OS_TEST_PATH=./castellan/tests/functional
+  OS_TEST_PATH=./castellan/tests/functional
 commands =
-    {toxinidir}/tools/setup-vault-env.sh pifpaf -e VAULT_TEST run vault -- stestr run --concurrency=1 --slowest {posargs}
+  {toxinidir}/tools/setup-vault-env.sh pifpaf -e VAULT_TEST run vault -- stestr run --concurrency=1 --slowest {posargs}
 allowlist_externals =
   {toxinidir}/tools/setup-vault-env.sh
 
 [testenv:genconfig]
 commands =
-    oslo-config-generator --config-file=etc/castellan/functional-config-generator.conf
-    oslo-config-generator --config-file=etc/castellan/sample-config-generator.conf
+  oslo-config-generator --config-file=etc/castellan/functional-config-generator.conf
+  oslo-config-generator --config-file=etc/castellan/sample-config-generator.conf
 
 [flake8]
 # [H106] Don't put vim configuration in source files.