Fix passenv for tox4

Space seperated list for passenv is no longer acceptable in tox4. This
change fixes the formatting of the passenv list as per this new
standard.

This change also removes skipsdist=true, which causes issues for loading
extensions in tox4.

Change-Id: If541ae03133e3d4a02b38a3e02c13f0b6355e13f

tox.ini

@@ -2,7 +2,6 @@
 minversion = 3.1.0
 envlist = py3,pep8
 ignore_basepython_conflict = True
-skipsdist = True
 
 [testenv]
 basepython = python3
@@ -10,7 +9,13 @@ usedevelop = True
 setenv =
    VIRTUAL_ENV={envdir}
    PYTHONWARNINGS=default::DeprecationWarning
-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
 deps =
        -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/requirements.txt