diamondd: Fixed search ID logging in start RPC
diamondd: Fixed search ID logging in start RPC

Since the search ID used to be an integer value, diamondd logged it
using the %d specifier. Change it to %s to log UUID strings.

cmusatyalab/opendiamond,cmusatyalab/opendiamond,cmusatyalab/opendiamond,cmusatyalab/opendiamond,cmusatyalab/opendiamond