correct management of one directional segments
    
        this patch contains the following improvements:
        check for existing segments works for all combinations of one directional and bidirectional segments
        rdns of replication agreements generated from one directional segments are preserves after
            merging of segments, so that deletion of the segment deletes the corresponding replication
            agreements
    
    Reviewed-By: Thierry Bordaz <tbordaz@redhat.com>