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

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-minversion = 3.1
+minversion = 3.18
 skipsdist = True
 envlist = pep8,py38
 ignore_basepython_conflict = True
@@ -7,7 +7,7 @@ ignore_basepython_conflict = True
 [testenv]
 basepython = python3
 usedevelop=True
-whitelist_externals = find
+allowlist_externals = find
                       rm
 deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/requirements.txt
@@ -71,14 +71,14 @@ commands =
   sphinx-build -W --keep-going -b html doc/source doc/build/html
 
 [testenv:pdf-docs]
-whitelist_externals = make
+allowlist_externals = make
 deps = {[testenv:docs]deps}
 commands =
   sphinx-build -W --keep-going -b latex doc/source doc/build/pdf
   make -C doc/build/pdf
 
 [testenv:genconfig]
-whitelist_externals = which
+allowlist_externals = which
 commands=
   oslo-config-generator --config-file etc/oslo-config-generator/kolla-build.conf