Adds a script to unmount any mount points in your boards image dir and free loopback devices

src/scripts/clean_loopback_devices

Index: src/scripts/clean_loopback_devices
diff --git a/src/scripts/clean_loopback_devices b/src/scripts/clean_loopback_devices
new file mode 100755
index 0000000000000000000000000000000000000000..4fbb5549aa27c6307ec4b5f98a2efd196be9170c
--- /dev/null
+++ b/src/scripts/clean_loopback_devices
@@ -0,0 +1,34 @@
+# Copyright (c) 2010 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.
+#
+# Force cleans loopback devices from within your chroot environment.  This
+# script is to help mitigate losing loopback devices on build_images
+# failures.  This script only affects mountpoints and loopback devices
+# that were created within this chroot.
+
+# Load common constants.  This should be the first executable line.
+# The path to common.sh should be relative to your script's location.
+. "$(dirname "$0")/common.sh"
+
+# Script must be run inside the chroot.
+assert_inside_chroot
+
+DEFINE_string output_root "$DEFAULT_BUILD_ROOT/images" \
+  "Directory in which to place image result directories (named by version)"
+DEFINE_string board "$DEFAULT_BOARD" \
+  "The board to build an image for."
+
+OUTPUT_DIR="${FLAGS_output_root}/${FLAGS_board}"
+
+echo "This will unmount any directory under $OUTPUT_DIR:"
+read -p "Are you sure (y/N)? " SURE
+SURE="${SURE:0:1}" # Get just the first character
+if [ "${SURE}" != "y" ]
+then
+  echo "Ok, better safe than sorry."
+  exit 1
+fi
+
+sudo umount "$OUTPUT_DIR"/*/* 2> /dev/null
+sudo losetup -d /dev/loop* 2> /dev/null