MB-100 Make xdcr logging don't repeat itself.

Change-Id: I9ee6b338db022d8ffeaf54f22d19291955e95b50
Reviewed-on: http://review.couchbase.org/28315
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>