Add migration script for helping with update of autotest-chrome.

With CL:59491, autotest-telemetry and autotest-chrome are again
being split into two separate ebuilds, so this means that we need
to uninstall the old version of autotest-chrome before we can install
the new version of autotest-telemetry. Do so.

BUG=chromium:59491
TEST=Run it locally.

Change-Id: I642bdf7faf17c6e9b917e61974726c14f1572011
Reviewed-on: https://gerrit.chromium.org/gerrit/59497
Reviewed-by: David James <davidjames@chromium.org>
Tested-by: David James <davidjames@chromium.org>
diff --git a/chroot_version_hooks.d/59_upgrade_autotest_pkgs b/chroot_version_hooks.d/59_upgrade_autotest_pkgs
new file mode 100644
index 0000000..d254a2c
--- /dev/null
+++ b/chroot_version_hooks.d/59_upgrade_autotest_pkgs
@@ -0,0 +1,32 @@
+# Copyright (c) 2013 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.
+
+# Remove old versions of autotest-chrome.
+opkg="chromeos-base/autotest-chrome"
+
+export CLEAN_DELAY=0
+
+update() {
+  local root=$1 board=$2 emerge
+
+  if [[ -z ${board} ]]; then
+    board="root"
+    emerge="sudo -E emerge"
+  else
+    emerge="emerge-${board}"
+  fi
+
+  if portageq has_version ${root} ${opkg}; then
+    ${emerge} -Cq ${opkg}
+  fi
+}
+
+update / &
+
+for board_root in /build/*; do
+  board=${board_root##*/}
+  update ${board_root} ${board} &
+done
+
+wait