Use m2-master CNAME to make DB rotations neater.
This allows a master switch to be a DNS change plus a simple port 3306
tcp redirect with socat until TTL. Should also help if we switch to a
haproxy configuration in the future.

Change-Id: Iead9eb026bbef31188d6b106962b66727e7d04c5
Merge "Use m2-master CNAME to make DB rotations neater. This allows a master switch to be a DNS change plus a simple port 3306 tcp redirect with socat until TTL. Should also help if we switch to a haproxy configuration in the future." into production