Ticket 477779 - Need to lock server list when removing list
    
    Description:  Need to hold the write lock when deleting the server list.
                  There is no need to lock the list in the close function,
                  as all active threads should be stopped.  In 1.3.3, the
                  dynamic plugin feature will also safely handle the plugin
                  shutdown.
    
    https://fedorahosted.org/389/ticket/47779
    
    Reviewed by: tbordaz(Thanks!)
    
    (cherry picked from commit 2b98dcaf83fba3ea4fc52c2b8cad6deea02cb0e5)