Render bucket in Couchbase::Result#inspect

Change-Id: I70f287eea4d55145ffdfa57b46e670aea3e2e54d
Reviewed-on: http://review.couchbase.org/23702
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Sokolov Yura <funny.falcon@gmail.com>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>