MB-9096: bumped cluster compat mode to 3.0

Change-Id: Icde488250eb5a8608825a755d1cb45683ae699b5
Reviewed-on: http://review.couchbase.org/29319
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>