Comment 2 for bug 1679750

Another thing to note here is the nova-api service does not currently use the placement API for anything. If we fixed this by doing allocation cleanup from nova-api, we'd have to make nova-api dependent on placement, which is something we might not want to do since only nova-scheduler and nova-compute depend on placement today. We might be able to just fix this by doing a cleanup during init_host in the compute service.