Ticket 47710 - Missing warning for invalid replica backoff configuration
    
    Bug Description:  If you manaully edit the dse.ldif and set the minimum or
                      maximum backoff time to zero, a warning/error is not given.
                      At server startup the server thinks zero means the attribute
                      is not set, and then sets it to the default value without
                      logging a message.
    
    Fix Description:  Properly check if the attribute is present, and log an error
                      accordingly.
    
    https://fedorahosted.org/389/ticket/47710
    
    Jenkins: passed
    
    Reviewed by: nhosoi(Thanks!)