function mergeWithExistingDevice(lanDevice) {
  const existing = this.gladys.stateManager.get('deviceByExternalId', lanDevice.external_id);
  return existing || lanDevice;
}
@description Get all discovered devices, and if device already created, the Gladys device.
@param {object} lanDevice - Discovered device.
@returns {object} Device merged with Gladys existing one.
@example
const mergedDevice = lanManager.mergeWithExistingDevice(discorveredDevice)