[atomic] Space leak issue in new installs of the *previous* Fedora Atomic Host release

[Colin Walters <walters verbum org>]

TL;DR: If you did a *new* installation of the previous Fedora Atomic Host,
run:

ostree refs --delete fedora-atomic:fedora-atomic/25/x86_64/updates/docker-host

This command will do nothing and be safe if you *aren't* affected.

New installations as well as upgrades from older releases are not affected.

A bit more information in:
https://pagure.io/atomic-wg/issue/251

(However, if you want to participate in development, you'll likely be rebasing
 back/forth with the updates ref anyways, in which case there's no leak).