Ticket 47888 - DES to AES password conversion fails if a backend is empty
    
    Bug Description:  The process of converting DES passwords to AES can incorrectly
                      disable the DES plugin if an error is encountered.  In this case
                      it was because a backend was defined but was missing the top entry
                      which lead to an error 32 when searching for DES passwords.  This
                      causes the existing DES passwords to fail to decode.
    
    Fix Description:  There are two issues here.  One, we should ignore errors when
                      searching all the backends for passwords.  Two, we should only
                      disable the DES plugin if all the DES passwords were successfully
                      converted.
    
    https://fedorahosted.org/389/ticket/48777
    
    Reviewed by: nhosoi(Thanks!)