Make tox.ini tox 4.0 compatible

* passenv fixed as space separated list is not allowed any more
* doc target uses requirements from requirements.txt as well as
  doc/requirements
* skipsdist is not supported

Change-Id: Ib60d63499fd021d9ec25357d20685573b18ade3e

tox.ini

@@ -1,18 +1,23 @@
 [tox]
 minversion = 3.18.0
-skipsdist = True
 envlist = py{38,39},pep8,lower-constraints
 ignore_basepython_conflict=true
 
 [testenv]
 basepython = python3
 deps =
-  -r{toxinidir}/test-requirements.txt
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -r{toxinidir}/requirements.txt
+  -r{toxinidir}/test-requirements.txt
 usedevelop = True
 setenv = VIRTUAL_ENV={envdir}
          CEILOMETER_TEST_BACKEND={env:CEILOMETER_TEST_BACKEND:none}
-passenv = OS_TEST_TIMEOUT OS_STDOUT_CAPTURE OS_STDERR_CAPTURE OS_LOG_CAPTURE CEILOMETER_*
+passenv =
+    OS_TEST_TIMEOUT
+    OS_STDOUT_CAPTURE
+    OS_STDERR_CAPTURE
+    OS_LOG_CAPTURE
+    CEILOMETER_*
 commands =
    stestr run {posargs}
    oslo-config-generator --config-file=etc/ceilometer/ceilometer-config-generator.conf
@@ -48,8 +53,9 @@ commands = oslo-config-generator --config-file=etc/ceilometer/ceilometer-config-
 [testenv:docs]
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -r{toxinidir}/requirements.txt
   -r{toxinidir}/doc/requirements.txt
-commands = sphinx-build -b html doc/source doc/build/html
+commands = sphinx-build --keep-going -b html -j auto doc/source doc/build/html
 setenv = PYTHONHASHSEED=0
 
 [testenv:pdf-docs]
@@ -61,7 +67,9 @@ commands =
   make -C doc/build/pdf
 
 [testenv:debug]
-commands=
+allowlist_externals =
+  find
+commands =
   find . -type f -name "*.pyc" -delete
   oslo_debug_helper {posargs}