Avoid stack overflow in LoadBalancer with CACHE_DB WAN/server cache

Avoid stack overflow in LoadBalancer with CACHE_DB WAN/server cache

* Add the ability to expose key BagOStuff attributes like whether the
  emulation SQL cache is being used. Several callers use hacks to detect
  this and can be updated later.
* Fallback to a safe empty WAN cache in the CACHE_DB case. This fixes
  a regression from f4bf52e8438.
* Also add this protection to the server cache, which could break
  similarly before too.
* Also fix CACHE_ANYTHING by avoid the recursion risk from
  fc1d4d796024 by just checking the disabled service map.

Bug: T123829
Bug: T141804
Change-Id: I17ee26138f69e01ec1aaddb55ab27caa4d542193