tox: delete all pyc before running test
tox: delete all pyc before running test

Delete python bytecode before every test run.
Because python creates pyc files during tox runs,
certain changes in the tree, like deletes of files,
or switching branches, can create spurious errors.

Change-Id: I670f485e9d4cf69abf9be30d800f4e9f27eaac3b
Closes-Bug: #1558603

openstack/kolla-mesos,openstack/kolla-mesos,asalkeld/kolla-mesos,openstack/kolla-mesos