Fix openstack-tox* failures

Looks like tox-extra plugin breaks openstack-tox*
jobs. Not sure if this is regression. I don't see
it being used in any other openstack projects.
Let's drop it.

Also cleans up things in setup.py.

Closes-Bug: #1998074
Change-Id: I154bfc36cc56f6b5425ec6bf805a290973203ba1
(cherry picked from commit 889dffa6a8a65d50d418c3724abb1912d5d4e882)

setup.py

@@ -16,14 +16,6 @@
 # THIS FILE IS MANAGED BY THE GLOBAL REQUIREMENTS REPO - DO NOT EDIT
 import setuptools
 
-# In python < 2.7.4, a lazy loading of package `pbr` will break
-# setuptools if some other modules registered functions in `atexit`.
-# solution from: http://bugs.python.org/issue15881#msg170215
-try:
-    import multiprocessing  # noqa
-except ImportError:
-    pass
-
 setuptools.setup(
     setup_requires=['pbr>=2.0.0'],
     py_modules=[],

tox.ini

@@ -2,9 +2,6 @@
 minversion = 3.18.0
 skipsdist = True
 envlist = pep8,py,tht
-requires =
-    # extra plugin returns error if git reports untracked or dirty files
-    tox-extra>=0.0.0
 
 [testenv]
 basepython = python3
@@ -17,6 +14,7 @@ commands =
   stestr run {posargs}
   stestr slowest
 setenv =
+  VIRTUAL_ENV={envdir}
   LC_ALL=en_US.UTF-8
 
 [testenv:venv]