code: function set(interface, variable, value, callback) {
      var command = ['wpa_cli -i',
                   interface,
                   'set',
                   variable,
                   value ].join(' ');
  
      return this.exec(command, parse_command_interface(callback));
  }
docs: /* others commands not tested
  ap_scan 1
  set_network 0 0 scan_ssid 1
  
  
  set: set,
  add_network: add_network,
  set_network: set_network,
  enable_network: enable_network