import lib/oslo so we can clean it up

we were calling cleanup_oslo, however we weren't importing
lib/oslo, so that was just throwing an error message and moving on.

Let's stop doing that and actually clean up oslo.

Change-Id: I48340a8b3d5b50477fb5a7e2ce0bed27deb3ec01
Merge "import lib/oslo so we can clean it up"
Merge branch 'master' of github.com:openstack-dev/devstack