       ...
     ]

Result (when action=='start'; only returns after scan completes):
{                                 (json object)
  "success" : true|false,         (boolean) Whether the scan was completed
  "txouts" : n,                   (numeric) The number of unspent transaction outputs scanned
  "height" : n,                   (numeric) The block height at which the scan was done
  "bestblock" : "hex",            (string) The hash of the block at the tip of the chain
  "unspents" : [                 