CHERRY-PICK: make_factory_toolkit: add installed version tag

Currently the version tag is only present in the factory toolkit, but
not after the toolkit is installed. Let's also install it so that we
know what version of factory toolkit we are using.

BUG=chrome-os-partner:28102
TEST=Build factory toolkit and check usr/local/factory/TOOLKIT_VERSION

Original-Change-Id: I372cc8b730bc6a8b07abe69b8b9d2b367aed9dac
Signed-off-by: Vic (Chun-Ju) Yang <victoryang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/197192
Reviewed-by: Mike Frysinger <vapier@chromium.org>
(cherry picked from commit bc6607e0137524b2bf5425c5bc2d7aced5581840)

Change-Id: I8bb3ecf363c47ffe1cd6618e342ccbc9421cb3c3
Reviewed-on: https://chromium-review.googlesource.com/197953
Commit-Queue: Bowgo Tsai <bowgotsai@chromium.org>
Tested-by: Bowgo Tsai <bowgotsai@chromium.org>
Reviewed-by: Vic Yang <victoryang@chromium.org>
diff --git a/make_factory_toolkit.sh b/make_factory_toolkit.sh
index c0515d7..4fafc04 100755
--- a/make_factory_toolkit.sh
+++ b/make_factory_toolkit.sh
@@ -69,7 +69,10 @@
     local builder="$(whoami)@$(hostname)"
     local id_str="${FLAGS_board} Factory Toolkit ${timestamp} ${builder}"
   fi
-  echo "${id_str}" >"${temp_pack_root}/VERSION"
+
+  local version_tag="usr/local/factory/TOOLKIT_VERSION"
+  echo "${id_str}" | sudo_clobber "${temp_pack_root}/${version_tag}"
+  ln -s "${version_tag}" "${temp_pack_root}/VERSION"
 
   local output_toolkit="${output_dir}/install_factory_toolkit.run"
   "${temp_pack_root}/usr/local/factory/py/toolkit/installer.py" \