Ticket #47400 - MMR stress test with dna enabled causes a deadlock
    
    Bug description: Under the heavy add/delete posix user entries,
    dna_update_config_event causes a deadlock.
    
    Fix description: dna_update_config_event starts transaction
    before updating the shared config entry to avoid the deadlock
    situation.
    
    https://fedorahosted.org/389/ticket/47400
    
    Reviewed by Rich (Thank you!!)