tox: Bump minimum to v4

This is what everyone is using anyway. Reflect that. We also modify
indentation so that it is consistent throughout the file.

Change-Id: I070aa92aa02101b89ad7e3180643b25a5c53f5b2
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

tox.ini

@@ -1,16 +1,11 @@
 [tox]
-minversion = 3.18.0
+minversion = 4.6
 envlist = py3,pep8
-skipsdist = True
-# this allows tox to infer the base python from the environment name
-# and override any basepython configured in this file
-ignore_basepython_conflict=true
 
 [testenv]
-basepython = python3
-usedevelop = True
-install_command = pip install {opts} {packages}
-setenv = VIRTUAL_ENV={envdir}
+usedevelop = true
+setenv =
+  VIRTUAL_ENV={envdir}
   ZAQAR_TESTS_CONFIGS_DIR={toxinidir}/zaqar/tests/etc/
   ZAQAR_TEST_MONGODB=1
   ZAQAR_TEST_SLOW=1
@@ -25,10 +20,10 @@ commands =
   stestr run --serial --slowest {posargs}
 
 [testenv:integration]
-setenv = {[testenv]setenv}
+setenv =
+  {[testenv]setenv}
   ZAQAR_TEST_INTEGRATION=1
   OS_TEST_PATH=./zaqar/tests/functional
-commands = stestr run --serial --slowest {posargs}
 
 [testenv:pep8]
 commands =
@@ -68,7 +63,8 @@ commands =
 # This environment is called from CI scripts to test and publish
 # the API Ref to docs.openstack.org.
 #
-allowlist_externals = bash
+allowlist_externals =
+  bash
   rm
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}