gooftool: unmount stateful partition

The original encstateful unmount sequence calling 'mount-encrypted
umount' from chromeos_shutdown won't work on our Python version
wipe_in_place. This results in a repairing message will show up when
booting into release partition first time after wiping. So we change to
manually unmount encstateful instead of calling 'mount-encrypted
umount'.

BUG=chrome-os-partner:56800
TEST=manually

Change-Id: If085962e5311ba3c7e0ed5bfc22c28e76674acb6
Reviewed-on: https://chromium-review.googlesource.com/383551
Reviewed-by: Shun-Hsing Ou <shunhsingou@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Youcheng Syu <youcheng@google.com>
Tested-by: Youcheng Syu <youcheng@google.com>
(cherry picked from commit 764aed70da302b0a83899354a8faddf8d9643eae)
Reviewed-on: https://chromium-review.googlesource.com/384751
Commit-Ready: Youcheng Syu <youcheng@google.com>
1 file changed