[autotest] modification to 102 migration script

Merge two alter statement into one, which makes it
faster.

with 81664102 rows in tko_tests, it takes 9 hours 22mins

TEST=database/migrate.py sync
database/migrate.py sync 101
BUG=None
DEPLOY=migrate

Change-Id: Ic52ac126a6ba6175f7f0ad445be15821da988e5c
Reviewed-on: https://chromium-review.googlesource.com/275744
Tested-by: Fang Deng <fdeng@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Fang Deng <fdeng@chromium.org>
1 file changed