Follow up on 1146

[ShlomiD83]

@ShlomiD83 #1491 provides the option to use a short-lived container to orchestrate the self-update process. Despite being experimental, I'm hoping that it provides a more reliable method for self-updates and should alleviate many of the problems noted in this thread.

Originally posted by @nicholas-fedor in #1146

Watchtower seems to update but old image isn't pruned, and the only notification i receive is when Watchtower spins back up.
No "new image was found/old image pruned/old container was removed" notifications.