Load presets from disk.

            Read JSON formatted preset data from the specified path,
            or the default location at ``/var/lib/sos/presets``.

            :param presets_path: a directory containing JSON presets.

def load_presets(self, presets_path=None):
        """Load presets from disk.

            Read JSON formatted preset data from the specified path,
            or the default location at ``/var/lib/sos/presets``.

            :param presets_path: a directory containing JSON presets.
        """
        presets_path = presets_path or self.presets_path
        if not os.path.exists(presets_path):
            return
        for preset_path in os.listdir(presets_path):
            preset_path = os.path.join(presets_path, preset_path)

            try:
                preset_data = json.load(open(preset_path))
            except ValueError:
                continue

            for preset in preset_data.keys():
                pd = PresetDefaults(preset, opts=SoSOptions())
                data = preset_data[preset]
                pd.desc = data[DESC] if DESC in data else ""
                pd.note = data[NOTE] if NOTE in data else ""

                if OPTS in data:
                    for arg in _arg_names:
                        if arg in data[OPTS]:
                            setattr(pd.opts, arg, data[OPTS][arg])
                pd.builtin = False
                self.presets[preset] = pd