Add functions for getting and setting controller roles of switches

    * add roles()
    * add get_role()
    * merge two versions of device_role()
    * comment out debug print statements
I added this grep string for consistency with other function, however I'm not sure this is needed/works in json mode. I think I'm doing something similar with the get_(role | device | port | link | ...) functions, but  return the whole object containing the match instead of just that line