Lower log level indicating sending/receiving mccouch messages

Change-Id: I18ca7bb5491a66a70964ebea359e530f06fcdea1
Reviewed-on: http://review.couchbase.org/34414
Reviewed-by: David Liao <david.liao@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>