It allows you to interact with devices managed by Mozpool.
The mozpool client allows you to interact with a Mozpool  instance through various APIs. This allows you to interact with various mobile devices that are managed by Mozpool. You can reboot the devices, query information about them and reimage them among many other actions.
This code is extracted from the initial work from jhopkins in mozharness . Not all of the API has been implemented as the initial work did but and the tests have not yet been ported.
jhopkins for initial work in mozharness. dustin, dividehex, ted and mcote for creating all the pieces in the Mozpool stack.