Ticket 48402 - v3 allow plugins to detect a restore or import
    
    Bug Description: RFE
                     plugins do not know if the database was imported or restored, it could require
                     different behaviour
    
    Fix Description: set flags in the backends whenever an import or restore was detected.
                     see: http://www.port389.org/docs/389ds/design/detect-startup-after-import-or-restore.html
    
    https://fedorahosted.org/389/ticket/48402
    
    Reviewed by: Noriko, thanks