[autotest] Fix db_optimize.

Took less than 2 minutes on x86-mario shard with over 3 months
history, ~80,000 rows in afe_jobs ~110,000 rows in
afe_special_tasks.

TEST=Run the script
BUG=chromium:455486

Change-Id: I0feb16e2da608e2db5194907be5d789dcf099fde
Reviewed-on: https://chromium-review.googlesource.com/259232
Tested-by: Fang Deng <fdeng@chromium.org>
Reviewed-by: Mungyung Ryu <mkryu@google.com>
Commit-Queue: Fang Deng <fdeng@chromium.org>
1 file changed