Make updater.py systemd script more robust

[hellais]

From https://paste.debian.net/hidden/344337da/ it seems like the systemd script for lepidopter-updater will stop trying to restart the updater if it fails for more than 3 times.

Moreover it seems like it tries to restart it in rapid sequential fashion.

It can happen that if the network is down (or github is down) it will fail to run the update script and hence fail to start.

We should:

• Add a delay of 60 seconds between restarts of the updater script
• Continue trying to restart it until we succeed