ClusterNode must be associated with a bucket once a bucket has been opened

"every bucket needs it's own set of nodes because SELECT_BUCKET is called and the connections are associated directly with a bucket. If so, this will fail if we try to open more than one bucket with a cluster object. I'll create a separate NCBC for the fix. ClusterNode.Owner was initially added to associate nodes with a bucket once a bucket has been bootstrapped."

https://github.com/couchbase/couchbase-net-client/blob/master/src/Couchbase/Core/ClusterNode.cs#L213-L218

https://github.com/couchbase/couchbase-net-client/blob/master/src/Couchbase/CouchbaseBucket.cs#L199