ReverseLookup: Don't return OpenCNAM errors as caller IDs

Skip the API entirely for non-US numbers, and ignore any non-200
bodies to avoid names of the "Limit Exceeded" variety

Change-Id: I1ea107ba828e6dba44fa0828ad5fedecb8faf4de
Only send US numbers to OpenCNAM

This fixes the "We currently accept only US numbers" that started a few
days ago. To reset the cached names, disable reverse lookup, make or
receive a phone call, then enable reverse lookup again.

Change-Id: I5e73e305389de125d581b9b16e687f296ad829b1