Make tox.ini tox 4.0.0 compatible

* removed skipsdist=True to make sure novaclient is available in the virtual
  env. The usedevelop and skipsdist does not work together any more
  tox-dev/tox#2730. For bindep we still don't
  need the current repo to be installed in the env so skipsdist added
  there.

Depends-On: https://review.opendev.org/c/zuul/zuul-jobs/+/866943
Change-Id: I979b91570c7b60273f35fbdf8464f6a9ee2007d6

tox.ini

@@ -1,7 +1,6 @@
 [tox]
 envlist = py3,pep8,docs
 minversion = 3.18.0
-skipsdist = true
 ignore_basepython_conflict = true
 
 [testenv]
@@ -100,4 +99,6 @@ import_exceptions = novaclient.i18n
 # 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