Zen: Serialize notify conditions calls, defer subscription.

 - Don't subscribe/unsubscribe to new rules until the config has
   been set, avoids race conditions.
 - Process all condition updates on the same thread.
 - Add the schedule provider's next alarm state to dumpsys.

Bug: 21111868
Change-Id: I389f4a4905a56d6c976f01408f48f87230109aba