NCBC-375: preferring ipv4-address

See http://www.couchbase.com/issues/browse/NCBC-375
Preferring ipv4-adress over ipv6 
(see also http://www.couchbase.com/issues/browse/MB-6378 and http://www.couchbase.com/communities/q-and-a/net-client-wont-communicate-cluster-successfully-configured-hostnames?current=node/640)