serverinit: support sync queues on database in genconfig

So now the GCE install with MySQL can keep its sync-to-index queue on the
same MySQL instance.

Change-Id: I75357d8e6e24bf1469bb617eb46803c11d0936d8
GCE: keep sync-to-index queue on MySQL

Change-Id: I660894ebd03fb04beaa852d92073fb2ad46a98c5