Ticket 48035 - nunc-stans - Revise shutdown sequence
    
    Description:  When we notify nunc-stans to stop (ns_set_shutdown),
                  we should first stop the listeners to prevent new connections
                  from being accepted.  To do this we need to move the
                  listener counter and indexes to globals so we can easily
                  clean things up in ns_set_shutdown().
    
    https://fedorahosted.org/389/ticket/48035
    
    Reviewed by: rmeggins(Thanks!)