Bump the semaphore for infra-prod jobs to max: 2 so that up to two infra
prod jobs can run in parallale on bridge at the same time. Note we
should land this after we are happy with the new setup's locking and
pausing.
Change-Id: Icce98bb495d5edd9256f8e1d65d88b2f9d879132
611bfce7b6