Fix docs build for tox4

Replace deprecated whitelist_externals with allowlist_externals.
Drop skipsdist = True setting.

Change-Id: Idd797022d7504efc676dbfbe8e3e9da42f26f1e0

tox.ini

@@ -1,7 +1,6 @@
 [tox]
 envlist = pep8,py38,py36-local,eslint,karma-local,docs-local,releasenotes,lower-constraints-local
 minversion = 2.3.2
-skipsdist = True
 
 [testenv]
 usedevelop = True
@@ -57,7 +56,7 @@ commands =
 
 [testenv:eslint]
 basepython = python3
-whitelist_externals =
+allowlist_externals =
   npm
 commands =
   npm install
@@ -68,7 +67,7 @@ commands =
 # Horizon from master is needed to be cloned into ../horizon on both local and CI.
 [testenv:karma]
 basepython = python3
-whitelist_externals =
+allowlist_externals =
   {[testenv:eslint]whitelist_externals}
 commands =
   npm install
@@ -76,14 +75,14 @@ commands =
 
 [testenv:karma-local]
 basepython = python3
-whitelist_externals =
+allowlist_externals =
   {[testenv:eslint]whitelist_externals}
 commands =
   {[testenv:karma]commands}
 
 [testenv:docs]
 basepython = python3
-whitelist_externals =
+allowlist_externals =
   rm
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
@@ -96,7 +95,7 @@ commands=
 basepython = python3
 envdir = {toxworkdir}/docs
 deps = {[testenv:docs]deps}
-whitelist_externals =
+allowlist_externals =
   make
 commands =
   sphinx-build -W --keep-going -b latex doc/source doc/build/pdf