Fix DNS zone --allow-dynupdate option behavior
    
    --allow-dynupdate was implemented as a Flag parameter type, which
    is not convenient for LDAP attributes. When a DNS zone with
    permitted dynamic updates was modified and the --allow-dynupdate
    flag was not set, dynamic updates were turned off.
    
    This patch changes the option type to Bool parameter type which
    behaves according to user expectations when modifying the zone.
    
    https://fedorahosted.org/freeipa/ticket/2039