[autotest] Setup chromeos_lab_servers database

This CL adds necessary script to create a chromeos_lab_servers database when
setting up Autotest.

This CL also changes the database_connection module so that any database
connection created by a given configure section will be force to use the
database credential defined in AUTOTEST_WEB (the AFE database).

design doc:
https://docs.google.com/a/google.com/document/d/1fqeXZElMkx5lVEh8xSdNMDn88LE6xJLkU-5vc3iVmOw/edit#

BUG=chromium:424700
TEST=locally run:
./site_utils/setup_dev_autotest.sh -p autotest -a /usr/local/autotest/
./database/migrate.py sync 0 -d AUTOTEST_SERVER_DB
./database/migrate.py sync 1 -d AUTOTEST_SERVER_DB

Confirm the database and tables are created for version 1 and deleted for version 0.

DEPLOY=migrate_server_db

Change-Id: Iea923b2bd5eca81689ac888322f7ae66e6938f10
Reviewed-on: https://chromium-review.googlesource.com/225971
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Prashanth B <beeps@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
diff --git a/global_config.ini b/global_config.ini
index e56b661..52cdeba 100644
--- a/global_config.ini
+++ b/global_config.ini
@@ -43,6 +43,9 @@
 global_db_min_retry_delay:
 global_db_max_retry_delay:
 
+[AUTOTEST_SERVER_DB]
+database: chromeos_lab_servers
+
 [SHARD]
 # If this is not None, the instance is considered a shard.
 # The value should be the hostname of the local shard.
@@ -102,6 +105,10 @@
 # Time in hours to wait before giving up on crash collection.
 crash_collection_hours_to_wait: 0.001
 
+# If True, use autotest_server_db to verify the host before running services
+# like scheduler, host-scheduler and suite-scheduler.
+use_server_db: False
+
 [SCHEDULER]
 die_on_orphans: False
 enable_scheduler: True