MT#9579 add option database.central.dbmaster

For Carrier 3.x only, but it is not harmful for CE/PRO.
It specifies the host for MySQL central->local replication.

Change-Id: I29cdbfa7b47e44f23e79aed1ff9cbae1549ca075
(cherry picked from commit 7e9962bbed471642595e5a9b9bbfa76844ec3b4c)