Cells: Fix for relaying instance info_cache updates

The update_cells argument was ignored in db/api.py.  The API cell when
doing an update calls this with False to prevent relaying the request
back to itself... but it was being relayed anyway.

Change-Id: I5a40c878a547e81605dc40f0077b7c6e20ee3ad4
Merge "Cells: Fix for relaying instance info_cache updates"