Clean out apt index caches at end of image build

Apt gets confused if it talks to a mirror with an older index than the
index currently cached by apt. This can happen when image builds use a
newer index than the booted image. Avoid these problems entirely by
removing those index caches at the end of image building.

Change-Id: I245d516ee8a44831b2c29612b782bad555c48a3f
Co-Author: Clark Boylan <clark.boylan@gmail.com>
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

diskimage_builder/elements/debootstrap/cleanup.d/99-clean-up-cache

@@ -0,0 +1,25 @@
+#!/bin/bash
+#
+# Copyright 2016 Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+#
+if [ ${DIB_DEBUG_TRACE:-1} -gt 0 ]; then
+    set -x
+fi
+set -eu
+set -o pipefail
+
+# NOTE(pabelanger): Remove cached info about APT repositories, as it will go
+# stale fast.
+sudo rm -rf $TARGET_ROOT/var/lib/apt/lists/*