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: I86640fc7ae5565838c701974252a5775d1582eb4

tox.ini

@@ -1,12 +1,11 @@
 [tox]
 minversion = 2.0
 envlist = py38,pep8,migration
-skipsdist = True
 
 [testenv]
 usedevelop = True
 install_command = pip install {opts} {packages}
-whitelist_externals = bash
+allowlist_externals = bash
                       find
                       rm
 setenv =
@@ -22,7 +21,13 @@ commands =
   stestr run {posargs}
   stestr slowest
 
-passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
+passenv =
+  http_proxy
+  HTTP_PROXY
+  https_proxy
+  HTTPS_PROXY
+  no_proxy
+  NO_PROXY
 
 [testenv:pep8]
 basepython = python3
@@ -64,7 +69,7 @@ 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
@@ -158,6 +163,8 @@ commands =
 # dependencies are missing! This also means that bindep must be installed
 # separately, outside of the requirements files.
 deps = bindep
+skipsdist=True
+usedevelop=False
 commands = bindep test
 
 [testenv:fullstack]