improve system node identification: use port-group prop

[x37v]

{
  "FULL_PATH": "/rnbo/jack/info/ports/properties",
  "DESCRIPTION": "Ports and a list of their properties",
  "CONTENTS": {
    "system:capture_1": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/system:capture_1",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/port-group\":\"rnbo-graph-user-io\",\"physical\":true,\"terminal\":true}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    },
    "system:capture_2": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/system:capture_2",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/port-group\":\"rnbo-graph-user-io\",\"physical\":true,\"terminal\":true}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    },
    "system:playback_1": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/system:playback_1",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/port-group\":\"rnbo-graph-user-io\",\"physical\":true,\"terminal\":true}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    },
    "system:playback_2": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/system:playback_2",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/port-group\":\"rnbo-graph-user-io\",\"physical\":true,\"terminal\":true}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    },
    "snd-0:out1": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/snd-0:out1",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/pretty-name\":\"left\"}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    },
    "snd-0:out2": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/snd-0:out2",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/pretty-name\":\"right\"}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    },
    "snd-1:out1": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/snd-1:out1",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/pretty-name\":\"left\"}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    },
    "snd-1:out2": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/snd-1:out2",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/pretty-name\":\"right\"}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    },
    "snd-2:out1": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/snd-2:out1",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/pretty-name\":\"left\"}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    },
    "snd-2:out2": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/snd-2:out2",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/pretty-name\":\"right\"}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    },
    "snd-3:out1": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/snd-3:out1",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/pretty-name\":\"left\"}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    },
    "snd-3:out2": {
      "FULL_PATH": "/rnbo/jack/info/ports/properties/snd-3:out2",
      "TYPE": "s",
      "VALUE": "{\"http://jackaudio.org/metadata/pretty-name\":\"right\"}",
      "ACCESS": 3,
      "CLIPMODE": "none",
      "DESCRIPTION": "JSON key/value object indicating Jack properties for this port"
    }
  }
}