Fix bug introduced by http://codereview.chromium.org/520004 in archive_build.sh step.

src/scripts/install_packages.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 install packages into the target root file system.
 #
 # NOTE: This script should be called by build_image.sh. Do not run this
 # on your own unless you know what you are doing.
@@ skipping 173 matching lines @@
 EOF
 
 # Install the kernel.
 sudo APT_CONFIG="$APT_CONFIG" apt-get --force-yes \
   install "linux-image-${KERNEL_VERSION}"
 
 # Clean up the apt cache.
 # TODO: The cache was populated by debootstrap, not these installs. Remove
 # this line when we can get debootstrap to stop doing this.
 sudo rm -f "${ROOT_FS_DIR}"/var/cache/apt/archives/*.deb
+# Need to rm read-only created lock files in order for archiving step to work
+sudo rm -rf "$APT_CACHE_DIR"
 
 # List all packages installed so far, since these are what the local
 # repository needs to contain.
 # TODO: Replace with list_installed_packages.sh when it is fixed up.
 dpkg --root="${ROOT_FS_DIR}" -l > \
   "${OUTPUT_DIR}/package_list_installed.txt"
 
 cleanup_rootfs_mounts
 trap - EXIT