implemented auth rpc in sasldauthd-port

Change-Id: I55fd5d1067a7eaac6cfa79934d83ec02cdc1b332
Reviewed-on: http://review.couchbase.org/44070
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>