tox: Use allowlist_externals instead of whitelist_externals
tox: Use allowlist_externals instead of whitelist_externals

whitelist_externals is now deprecated, use allowlist_externals
instead. see[0]

[0]: https://tox.readthedocs.io/en/latest/config.html

follow: https://review.opendev.org/c/openstack/kolla-ansible/+/791928

Change-Id: I511fa599f43c5376f841ec6d03e272243aaa2ba4

openstack/kolla,openstack/kolla