Add defaults for cros_make_image_bootable.

This will allow dev who didn't build an image to still use cros_make_image_bootable
to update their image -- including mod_image_for_test / image_to_vm.

Change-Id: I1ba4292223b28b21d5416745e7744641100fa4ad

BUG=7370
TEST=Ran image_to_vm with other image and image I built myself.  Also ran
cros_make_image_bootable directly on a the same two images.

Review URL: http://codereview.chromium.org/3569015

bin/cros_make_image_bootable

@@ -28,8 +28,9 @@ if [ $# -lt 2 ]; then
   exit 1
 fi
 
-BOOT_DESC_FILE="${1}/boot.desc"
+IMAGE_DIR="$(readlink -f "${1}")"
-IMAGE="${1}/${2}"
+BOOT_DESC_FILE="${IMAGE_DIR}/boot.desc"
+IMAGE="${IMAGE_DIR}/${2}"
 shift
 shift
 FLAG_OVERRIDES="${@}"
@@ -233,6 +234,16 @@ make_image_bootable() {
     -s "${FLAGS_statefulfs_mountpoint}"
 }
 
+# Use default of current image location if the output dir doesn't exist.
+if [ ! -d ${FLAGS_output_dir} ]; then
+  warn "Output dir not found, using ${IMAGE_DIR}."
+  FLAGS_output_dir="${IMAGE_DIR}"
+  FLAGS_rootfs_hash="${IMAGE_DIR}/rootfs.hash"
+  FLAGS_rootfs_mountpoint="${IMAGE_DIR}/rootfs_dir"
+  FLAGS_statefulfs_mountpoint="${IMAGE_DIR}/stateful_dir"
+  FLAGS_espfs_mountpoint="${IMAGE_DIR}/esp"
+fi
+
 # Create the directories if they don't exist.
 mkdir -p ${FLAGS_rootfs_mountpoint}
 mkdir -p ${FLAGS_statefulfs_mountpoint}