Enable fast build by default in build_image and mod_image_for_test.sh.

build_image

 #!/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 from within
 # a chromiumos setup. This assumes that all needed packages have been built into
 # the given target's root with binary packages turned on. This script will
 # build the Chrome OS image using only pre-built binary packages.
@@ skipping 41 matching lines @@
 DEFINE_integer rootfs_size 720 \
   "rootfs filesystem size in MBs."
 # ceil(0.1 * rootfs_size) is a good minimum.
 DEFINE_integer rootfs_hash_pad 8 \
   "MBs reserved at the end of the rootfs image."
 DEFINE_integer statefulfs_size 1024 \
   "stateful filesystem size in MBs."
 DEFINE_boolean preserve ${FLAGS_FALSE} \
   "Attempt to preserve the previous build image if one can be found (unstable, \
 kernel/firmware not updated)"
-DEFINE_boolean fast ${FLAGS_FALSE} \
-  "Call many emerges in parallel (unstable)"
+DEFINE_boolean fast ${DEFAULT_FAST} \
+  "Call many emerges in parallel"
 
 DEFINE_string usb_disk /dev/sdb3 \
   "Path syslinux should use to do a usb boot. Default: /dev/sdb3"
 
 DEFINE_boolean enable_rootfs_verification ${FLAGS_FALSE} \
   "Default all bootloaders to use kernel-based root fs integrity checking."
 DEFINE_integer verity_error_behavior 2 \
   "Kernel verified boot error behavior (0: I/O errors, 1: reboot, 2: nothing) \
 Default: 2"
 DEFINE_integer verity_depth 1 \
@@ skipping 691 matching lines @@
   echo "Developer image created as ${DEVELOPER_IMAGE_NAME}"
 fi
 
 print_time_elapsed
 
 echo "To copy to USB keyfob, OUTSIDE the chroot, do something like:"
 echo "  ./image_to_usb.sh --from=${OUTSIDE_OUTPUT_DIR} --to=/dev/sdX"
 echo "To convert to VMWare image, INSIDE the chroot, do something like:"
 echo "  ./image_to_vm.sh --from=${OUTSIDE_OUTPUT_DIR}"
 echo "from the scripts directory where you entered the chroot."