Ticket 534 - Add SASL mappings fallback
    
    Bug Description:  IPA team requested that the fallback feature be configurable.
    
    Fix Description:  Added new config setting under cn=config to turn feature "on",
                      the default is "off".
    
    https://fedorahosted.org/389/ticket/534
    
    Reviewed by: richm(Thanks Rich!)