Dns config ini format

    Configuration format changes for the dns
    control-node now take configuration in the standard ini format.
    Default configuration file is read off /etc/contrail/dns.conf
    
    One can override the values from the config file through command line option
    as well. e.g. --DEFAULT.log_level=DEBUG
    
    Use --help to see various options available. contrail-control package also
    places the default config file under /etc/contrail/dns.conf
    
    When changes are made to the configuration file, the process must be _restarted_
    to take effect. (service supervisord-control restart).