Make tox.ini tox 4.0.0 compatible

* removed skipsdist=True to make sure cloudkitty is available in the
  virtual env

* added find to allowed external commands in tox

* replaced full path to find for readability

Change-Id: I4211e9be3e170f8724246883768247727b1d5d0b
Co-Authored-By: Pierre Riteau <pierre@stackhpc.com>

tox.ini

@@ -1,12 +1,13 @@
 [tox]
 minversion = 3.18.0
-skipsdist = True
 envlist = py3,pep8
 ignore_basepython_conflict = True
 
 [testenv]
 basepython = python3
-allowlist_externals = rm
+allowlist_externals =
+    find
+    rm
 setenv = VIRTUAL_ENV={envdir}
          PYTHONWARNINGS=default::DeprecationWarning
 usedevelop = True
@@ -16,7 +17,7 @@ deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/up
        -r{toxinidir}/test-requirements.txt
 
 commands =
-  /usr/bin/find . -type f -name "*.py[co]" -delete
+  find . -type f -name "*.py[co]" -delete
   rm -f .testrepository/times.dbm
   stestr run {posargs}