Fix log message for remaining bytes to send to mccouch

In addition to improving the log message, backoff trying
to send the data to allow the other side to drain their
end.

Change-Id: Ibddfd9f87c1025d3256ad80f5e49516d56222e69
Reviewed-on: http://review.couchbase.org/40044
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>