chroot_upgrade: rename things before it's too late

The name chroot_upgrade is rather confusing since we already have
"chroot_update" and those two scripts will be chained. It was the
original name before update_chroot existed.

BUG=none
TEST=run the new one, see it work the same

Change-Id: I851fc4a0f28e32a9bbd01b2e4ddedbaffc6abf1c
Reviewed-on: http://gerrit.chromium.org/gerrit/876
Reviewed-by: David James <davidjames@chromium.org>
Tested-by: Zdenek Behan <zbehan@chromium.org>

run_chroot_version_hooks

@@ -25,7 +25,7 @@ DEFINE_boolean skipfirst "${FLAGS_FALSE}" \
 FLAGS "$@" || exit 1
 
 VERSION_FILE=/etc/cros_chroot_version
-UPGRADE_D="$(dirname ${0})/chroot_upgrade.d"
+UPGRADE_D="$(dirname ${0})/chroot_version_hooks.d"
 
 function update_version() {
   sudo touch ${VERSION_FILE}