Issue 50734 - lib389 creates non-SSCA cert DBs with misleading README.txt
    
    Bug Description:
    `NssSsl` always creates `README.txt` which describes the purpose of SSCA, even
    when creating only an instance-specific certificate database.
    
    Fix Description:
    Create the README.txt only when creating cert DB for a specified DS instance.
    
    Fixes https://pagure.io/389-ds-base/issue/50734
    
    Author: Matus Honek <mhonek@redhat.com>
    
    Review by: Mark, William (thanks!)