py3: ConfigParser: replace deprecated readfd with read
    
    ConfigParser.readfd() is deprecated in py3, we can use .read() which is
    compatible with py2
    
    https://fedorahosted.org/freeipa/ticket/4985
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>