The node resource(vcpu, memory and disk) used infomation need
to change when creating or deleting instances. Now Placement do
not send notifications, so there is not a good way to capture
the change. We remove these fields and leave the process to strategy.
Partially Implements: blueprint improve-compute-data-model
Change-Id: I3f9a3279a26f3df444117d9265e74cca57b38d6e
4e4cfc959b