MB-8663 Expose replication type in xdcr task.

Change-Id: I55f11c066d6916a8a588287d2c4b79a53eed0163
Reviewed-on: http://review.couchbase.org/28172
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>