Fix tox4 error

tox.ini started failing with Tox4 which had some
incompatible changes. One is passenv where we need
to pass each value in newline otherwise, it fails with
error:

 failed with pass_env values cannot contain whitespace,
 use comma to have multiple values in a single line,
 invalid values found.....

Fixing tox.ini for tox4 changes.

Change-Id: I0a377c9329cef8b251b800018fc0d7f784008329
(cherry picked from commit e2cd725)
(cherry picked from commit 022e150)
(cherry picked from commit 3f6c689)

Author: Ghanshyam Mann

tox.ini

@@ -2,7 +2,6 @@
 minversion = 3.18.0
 # python runtimes: https://governance.openstack.org/tc/reference/runtimes/ussuri.html
 envlist = functional-py38,py38,py36,pep8
-skipsdist = True
 skip_missing_interpreters = true
 # this allows tox to infer the base python from the environment name
 # and override any basepython configured in this file
@@ -33,7 +32,9 @@ commands =
 allowlist_externals = bash
                       find
                       rm
-passenv = *_proxy *_PROXY
+passenv =
+    *_proxy
+    *_PROXY
 
 [testenv:functional]
 # this will use whatever the system python3 is