Add tests for PELT
Created by: mdigiorgio
This PR adds a couple of tests for making sure PELT signals (right, util_avg_task only is tested) works as expected.
The tests rely on the PELT simulator that @derkling is adding to bart (see https://github.com/mdigiorgio/bart/tree/pelt_simulator). As a consequence, we should have that merged before we accept this.
I'm posting this now to get some initial feedback on the approach, that's why I set it as WIP.