Fix stale pyc issue for unit tests

See the following for more info:
* http://lists.openstack.org/pipermail/openstack-dev/2014-September/045845.html
* http://lists.openstack.org/pipermail/openstack-dev/2014-September/045873.html
* https://review.openstack.org/#/c/121044/

Change-Id: I98161082cd72b92a7af44f8be8b5a92328a72281

tox.ini

@@ -7,10 +7,13 @@ skipsdist = True
 usedevelop = True
 setenv = VIRTUAL_ENV={envdir}
 install_command = pip install -U {opts} {packages}
+whitelist_externals = find
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
        -r{toxinidir}/doc-requirements.txt
-commands = python setup.py testr --slowest --testr-args='{posargs}'
+commands =
+  find . -type f -name "*.pyc" -delete
+  python setup.py testr --slowest --testr-args='{posargs}'
 
 [testenv:cover]
 commands = python setup.py testr --coverage --testr-args='{posargs}'