tri_state.py: Adapt for Ubuntu Touch 20.04 (Focal)

Drafting until https://t.me/ubports_devel/70963 is solved:

(16.04) Device images are still built from those repos, only rootfs was disabled. We also would need to halt those jobs properly

Alternatively logic can be added to check if running on 20.04 vs 16.04 but after last OTA-25 it doesn't really make much sense anymore imo