Add board option to au test harness so that this works for others without a default board.

get_latest_image.sh

 #!/bin/bash
 
 # Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Prints the path to the most recently built image to stdout.
 
 # Load common constants.  This should be the first executable line.
 # The path to common.sh should be relative to your script's location.
 . "$(dirname "$0")/common.sh"
 
 get_default_board
 
 DEFINE_string board "$DEFAULT_BOARD" \
   "The name of the board to check for images."
 
 # Parse command line flags
 FLAGS "$@" || exit 1
 eval set -- "${FLAGS_ARGV}"
 
 # Check on the board that they are trying to set up.
 if [ -z "$FLAGS_board" ] ; then
-  echo "Error: --board required."
-  exit 1
+  die "Error: --board required."
 fi
 
 IMAGES_DIR="${DEFAULT_BUILD_ROOT}/images/${FLAGS_board}"
 
 # If there are no images, return nothing
 [ -d $IMAGES_DIR ] || exit 0
 
 # Use latest link if it exists, otherwise most recently changed dir
 if [ -L ${IMAGES_DIR}/latest ] ; then
   DEFAULT_FROM="${IMAGES_DIR}/`readlink ${IMAGES_DIR}/latest`"
 else
   DEFAULT_FROM="${IMAGES_DIR}/`ls -t $IMAGES_DIR | head -1`"
 fi
 
 echo $DEFAULT_FROM