Fix tox4 error

tox.ini started failing with tox4 which had some
incompatible changes. One of them is to allow
external command to run by adding them into allowlist_externals
and make passenv in new lines.

Fixing tox.ini for tox4 changes.

Change-Id: Ic10c68cf73f0e181c1182b348f49b9fff1f4cf24

tox.ini

@@ -1,7 +1,6 @@
 [tox]
 minversion = 2.0
 envlist = pep8,py3
-skipsdist = True
 ignore_basepython_conflict = true
 
 [testenv]
@@ -15,7 +14,9 @@ deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/up
 commands =
     find . -type f -name "*.pyc" -delete
     /bin/bash run_tests.sh -N --no-pep8 {posargs}
-whitelist_externals = find
+Allowlist_externals =
+  find
+  /bin/bash
 
 [testenv:pep8]
 commands =
@@ -42,7 +43,7 @@ commands =
   sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:debug]
-whitelist_externals = oslo_debug_helper
+Allowlist_externals = oslo_debug_helper
 commands = oslo_debug_helper -t mistraldashboard/test {posargs}
 
 [flake8]