precision topology_view caching

[eagmon]

If a '_generate' or '_divide' update is triggered it requires the expiration and re-caching of some topology_views. Currently, Store.apply_update will pass a view_expire flag (here) back to Engine, which triggers self.state.build_topology_views(): (here). This expires and re-caches ALL of the topology_views across the entire Store hierarchy. It would be more efficient if it knew to only expire and re-cache the topology_view of the subset of processes that are connected to the affected stores.