Fix a race in local settings caches

We send a handle to the generation tracker along with the first accessed
setting but don't send the generation id of when the setting was
actually looked up. So by the time the client gets the setting with the
generation tracker from which to get and cache the last generation the
setting may have changed. We need to pass the generation id along with
the value and the generation tracker.

bug:29458487

Change-Id: I0ac4955ba5b10b547f8fe653a7c28e048a4691eb