[ale] Make sink type part of sink module definition.

Change-Id: Iaa4ee6d43a585d2ab2295c4d4753669f4f60d64b
Reviewed-on: http://review.couchbase.org/37744
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>