Ticket 48961 - Fix lib389 minor issues shown by 48961 test
    
    Bug Description:  There were a small number of issues in lib389. Mainly in
    reporting of errors with replication and how we deleted values.
    
    Fix Description:  Fix the detection of a None to modify_s so that we can delete
    values. Fix error message for replication.
    
    https://fedorahosted.org/389/ticket/48961
    
    Author: wibrown
    
    Review by: spichugi (Thanks!)