build: Update build_image.sh for non-~/chromeos setups.

src/scripts/build_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.
 
 # Script to build a bootable keyfob-based chromeos system image.
 # It uses debootstrap (see https://wiki.ubuntu.com/DebootstrapChroot) to
 # create a base file system. It then cusotmizes the file system and adds
 # Ubuntu and chromeos specific packages. Finally, it creates a bootable USB
@@ skipping 256 matching lines @@
 dd if="$SYSLINUX_MBR" of="$MBR_IMG" bs=512 count=1 conv=sync
 # Create a partition table in the MBR.
 NUM_SECTORS=$((`stat --format="%s" "$ROOT_FS_IMG"` / 512))
 sudo sfdisk -H64 -S32 -uS -f "$MBR_IMG" <<EOF
 ,$NUM_SECTORS,L,-,
 ,$NUM_SECTORS,S,-,
 ,$NUM_SECTORS,L,*,
 ;
 EOF
 
-OUTSIDE_OUTPUT_DIR="~/chromeos/src/build/images/${IMAGE_SUBDIR}"
+OUTSIDE_OUTPUT_DIR="${EXTERNAL_TRUNK_PATH}/src/build/images/${IMAGE_SUBDIR}"
 echo "Done.  Image created in ${OUTPUT_DIR}"
 echo "To copy to USB keyfob, outside the chroot, do something like:"
 echo "  ./image_to_usb.sh --from=${OUTSIDE_OUTPUT_DIR} --to=/dev/sdb"
 echo "To convert to VMWare image, outside the chroot, do something like:"
 echo "  ./image_to_vmware.sh --from=${OUTSIDE_OUTPUT_DIR}"
 
 trap - EXIT