Update oslo-incubator common module

openstack/common/__init__.py was modified as part of a shift to add
basic Python 3 tests. Specifically,

commit c178e567cb48d3bc67dcf06bcbb4c6a97df9f434
Author: Julien Danjou <julien@danjou.info>
Date:   Wed Jun 12 17:57:00 2013 +0200

Change-Id: I87d83d5ff340713e2a4632088d6b665d2c71e57b