MB-9858 Fix request_remote_bucket_on_new_conn's return value.

It must be {ok, RemoteBucket} instead of
{ok, {RemoteCluster, RemoteBucket}}.

Change-Id: I28ad238b68172ef336d74678e4a1e86ca7e590fd
Reviewed-on: http://review.couchbase.org/31747
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>