MB-8665: encode json via somewhat faster ejson facility

Change-Id: Ia45dd76e4706133874716d2344c9c804773af6c4
Reviewed-on: http://review.couchbase.org/28956
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>