ResourceGroup update refactor

Reworks ResourceGroup.handle_update a little so we save the updated
properties in the resource object before processing the update.

This is required so we can have a hint property which specifies
victims to be removed on update

Change-Id: I4884a929ede1c6bff835fe789e5dd890a06831c2
blueprint: resourcegroup-force-remove
Merge "ResourceGroup update refactor"