listen all necessary notifications

In Watcher, it firstly builds compute CDM by collecting nova compute resource, later update the compute CDM by listening to nova notifications.
It has listened to following nova events,
* instance.update
* instance.delete.end
* compute.instance.update
* compute.instance.create.end
* compute.instance.delete.end
* compute.instance.live_migration.post.dest.end

In one cloud env, there would be many solutions, which would make the compute resource strongly relocated, such as 'auto-scaling' solution and 'compute-ha' solution.
If Watcher doesn't listen to all the notifications which represent that nova compute resource changes, the compute CDM will be stale, and doesn't work.