[autotest] Add server_attributes table to server database.

We need a table to store server attributes like max_processes for drone.

BUG=chromium:424778
TEST=run database migration and confirm tables are created/deleted.
    ./database/migrate.py sync 0 -d AUTOTEST_SERVER_DB
    ./database/migrate.py sync 2 -d AUTOTEST_SERVER_DB

Change-Id: I5d7247d422d18a83fe7fcaa1435483654f71062d
Reviewed-on: https://chromium-review.googlesource.com/230814
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Fang Deng <fdeng@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
1 file changed