Fixes for tox4

- Replace long deprecated whitelist_externals with allowlist_externals.
- Drop basepython option that is no longer needed.
- Invoke bash scripts with explicit bash command instead of allowlisting
  every single script.

Change-Id: I2b70ebb3b1ee94ad75e46295d788312c5e183748

tox.ini

@@ -4,12 +4,11 @@ envlist = linters,publishdocs
 skipsdist = True
 
 [testenv]
-basepython=python3
 setenv =
    VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/test-requirements.txt
 passenv = ZUUL_*
-whitelist_externals =
+allowlist_externals =
   bash
   cp
   mkdir
@@ -27,19 +26,19 @@ commands =
 commands =
   flake8
   doc8 doc
-  {toxinidir}/tools/glossary-sort.sh
+  bash {toxinidir}/tools/glossary-sort.sh
 
 [testenv:docs]
 commands =
-  {toxinidir}/tools/build-all-rst.sh
+  bash {toxinidir}/tools/build-all-rst.sh
 
 [testenv:pdfs]
 commands =
-  {toxinidir}/tools/build-all-rst.sh --pdf
+  bash {toxinidir}/tools/build-all-rst.sh --pdf
 
 [testenv:build]
 commands =
-  {toxinidir}/tools/build-rst.sh \
+  bash {toxinidir}/tools/build-rst.sh \
     doc/{posargs} \
     --build build \
     --target {posargs}
@@ -49,25 +48,25 @@ commands =
 # published on docs.openstack.org with just copying publish-docs/*
 # over.
 commands =
-  {toxinidir}/tools/publishdocs.sh
+  bash {toxinidir}/tools/publishdocs.sh
   whereto publish-docs/html/.htaccess publish-docs/html/redirect-tests.txt
   rm publish-docs/html/redirect-tests.txt
 
 [testenv:buildlang]
 # Run as "tox -e buildlang -- $LANG"
-whitelist_externals = doc-tools-check-languages
+allowlist_externals = doc-tools-check-languages
 commands =
   doc-tools-check-languages doc-tools-check-languages.conf test {posargs}
 
 [testenv:publishlang]
-whitelist_externals = doc-tools-check-languages
+allowlist_externals = doc-tools-check-languages
 commands =
   doc-tools-check-languages doc-tools-check-languages.conf publish all
 
 [testenv:generatepot-rst]
 # Generate POT files for translation, needs {posargs} like:
 # tox -e generatepot-rst -- user-guide
-commands = {toxinidir}/tools/generatepot-rst.sh openstack-manuals 1 {posargs}
+commands = bash {toxinidir}/tools/generatepot-rst.sh openstack-manuals 1 {posargs}
 
 [testenv:releasenotes]
 commands =