Use recovery.conf from Chromebook Recovery Utility to source recovery images

Right now the images are scraped from [cros-updates-serving](https://cros-updates-serving.appspot.com).

This can be unreliable and shouldn't be used when it can be sourced from the same place that the official recovery utility uses.

[The recovery.conf file can be found here](https://dl.google.com/dl/edgedl/chromeos/recovery/recovery.conf)