Disable automatic CoreOS updates in all-in-one image
From Slack, discussion at https://gitlab.slack.com/archives/C0SFP840G/p1517305944000071
IIRC you use CoreOS as the base, and this is default there. In packer script for shared runners images we're doing this:
message "Disable automatic updates..."
systemctl mask update-engine.service
systemctl mask locksmithd.service