tox: use allowlist_externals

Change-Id: I88c6a05d0813a685c28be9081f7a36a6a0c8711c

tox.ini

@@ -15,14 +15,17 @@ deps =
    -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
    -r{toxinidir}/requirements.txt
    -r{toxinidir}/test-requirements.txt
-whitelist_externals = find
-                      rm
+allowlist_externals =
+    find
+    rm
 commands =
     find . -type f -name "*.pyc" -delete
     rm -f .testrepository/times.dbm
     stestr run {posargs}
 
 [testenv:pep8]
+allowlist_externals =
+  {toxinidir}/tools/check_for_alembic_branches.sh
 commands =
   flake8
   {toxinidir}/tools/check_for_alembic_branches.sh
@@ -53,7 +56,7 @@ commands =
 
 [testenv:pdf-docs]
 deps = {[testenv:docs]deps}
-whitelist_externals =
+allowlist_externals =
   make
 commands =
   sphinx-build -W -b latex doc/source doc/build/pdf