Ticket 48184 - clean up and delete connections at shutdown (2nd try)
    
    Bug description:
        During shutdown we would not close connections.
        In the past this may have just been an annoyance, but now with the way
        nunc-stans works, io events can still trigger on open xeisting connectinos
        during shutdown.
    
        Because of NS dynamic it can happen that several jobs wants to work on the
        same connection. In such case (a job is already set in c_job) we delay the
        new job that will retry.
        In addition:
    	- some call needed c_mutex
    	- test uninitialized nunc-stans in case of shutdown while startup is not completed
    
    Fix Description:  Close connections during shutdown rather than
        leaving them alive.
    
    https://pagure.io/389-ds-base/issue/48184
    
    Reviewed by:
    	Original was Ludwig and Viktor
    	Second fix reviewed by Mark
    
    Platforms tested: F26
    
    Flag Day: no
    
    Doc impact: no
    
    (cherry picked from commit e562157ca3e97867d902996cc18fb04f90dc10a8)