This serverId value is used by notedb to identify the gerrit cluster
that notedb contents belong to. By default a random uuid is generated by
gerrit for this value. In order to avoid config management and gerrit
fighting over this value after we upgrade we set a value now.
This should be safe to land on 2.13 as old gerrit should ignore the
value.
Change-Id: I57c9b436a9d0d1dfe77eee907d50fc1dcda6ab12