Don't log metakv conflicts to the user log.
Don't log metakv conflicts to the user log.

Unfortunately, conflicts are way too common when cbft is used. So
metakv keys are treated specially: the conflict information will only
get logged to the debug log.

Change-Id: Ib6a19ac8fc76df4465ac753a0bcaa99da2aff84a
Reviewed-on: http://review.couchbase.org/63961
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>

ceejatec/ns_server,membase/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server