Branch: factory-scarlet-10211.B

What steps will reproduce the problem?
(1) Run RunInRebootSequence for 500 times

What is the expected result?
Pass the test

What happens instead?
FAILED: ShutdownError: Unable to read shutdown_time; unexpected shutdown during reboot?

Note
(1) The probability to reproduce this issue is quite low.
    I saw this issue after 474 successful reboot cycle.
(2) In "factory.log", there is a message "Graceful shutdown interrupted, shutting down abruptly." in the end of every Goofy session.
    This message is also in ToT factory toolkit.
(3) In "factory.log", it seems like to log of the second last Goofy session is corrupted. (All bytes belongs to it became '\0')
I suspect that we didn't flush file due to the abrupt shutdown so the shutdown_time and factory.log were corrupted.