MB-7491: use 2.0.1 as master heartbeat version

So that 2.0.1 will forcefully take mastership from 2.0.0 nodes.

Change-Id: I5bf0ddc6d27362646bc5e2694b6adf99e4165950
Reviewed-on: http://review.couchbase.org/23728
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>