Turn on pooled updating in canary.
Turn on pooled updating in canary.

This will concurrently download builds in test groups, instead
of serially download builds in concurrent test groups.

GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid