Convert some users to WANObjectCache for consistency

Convert some users to WANObjectCache for consistency

These callers don't need to do purges, but can still perfectly
take advantage of this instance over a plain BagOStuff. Namely:
* Replication and snapshot lag awareness
* Preemptive regeneration
* Easy process cache support

The idea is for there to only be one caching class/factory
to use, instead of having rules for picking which one to use.

Change-Id: I8e362df451c0c28731fc853c044c4c4b8e097f01