bp: MB-11137 Fix sending mail alerts for compound keys.

Change-Id: Ie2312d8aa4e7b26f958988427d57c8c399b62ce4
Orig-Reviewed-on: http://review.couchbase.org/37207
Orig-Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Orig-Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-on: http://review.couchbase.org/42854
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>