GUI LED status doesn't refresh if ledctl disables beacon

[warpmech]

There’s a minor problem in that if you:

1. Enable locate in the zfswatcher UI
2. Disable locate via ledctl on the CLI
3. zfswatcher UI still shows the beacon active even on refresh
   a. click to clear indicator; the LED stays off (at least the function is not inverted)

[snabb]

Zfswatcher goes out of sync with the real led status because it does not poll the LEDs to update its knowledge about their status. Ledctl does not provide any way for getting this information. I have previously considered implementing the ledctl functionality built-in to zfswatcher but it is a lot of work.

Patches are welcome :)