chameleon-updater: Guard updating process

Move the updater to a deamon for keeping running when we do reboot.
Check the updating process in stop operation, because it will be
executed during reboot process.

BUG=chromium:718064
TEST=Reboot chameleon board during updating process. Check it will wait
until the update process done. Create a fake file and check timeout
works.

Change-Id: I78ff993bb594ccc1ba10d7a2f9db34c8ace45285
Reviewed-on: https://chromium-review.googlesource.com/499831
Commit-Ready: Hsu Wei-Cheng <mojahsu@chromium.org>
Tested-by: Hsu Wei-Cheng <mojahsu@chromium.org>
Reviewed-by: Wai-Hong Tam <waihong@google.com>
3 files changed