Use get_replication_plugin_name in LDAP updater
    
    This allows for a consistent way to retrieve the value from
    LDAP. The method is used to find an existing entry. It is not usable
    to add or remove entries.
    
    Moving it in the code allows the value to always be set in the
    substitution dictionary and not rely on a specific caller.
    
    It was moved to installutils.py to avoid circular import.
    
    https://pagure.io/freeipa/issue/8885
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>