Ticket 49448 - dynamic default pw scheme based on environment.
    
    Bug Description:  In some cases the hardcoded default pw scheme
    is not available, IE FIPS mode doesn't support pbkdf2. In this
    case we need to support returning an appropriate scheme based
    on environment.
    
    Fix Description:  Add a new scheme name called "DEFAULT" with
    a mechanic that pw_name2scheme will use this with environment
    information to return an appropriate scheme.
    
    https://pagure.io/389-ds-base/issue/49448
    
    Author: wibrown
    
    Review by: mreynolds, spichugi (Thanks!)