testing stream: 31.20191211.1 and manual intervention

[Luca BRUNO]

Hi all,
we recently released FCOS 31.20191127.1 on the testing stream,
and we later realized that it may have broken rpm-ostreed on some
nodes: https://github.com/coreos/fedora-coreos-tracker/issues/322

Today we released 31.20191211.1 which fixes that buggy behavior.
It is currently rolling out on the testing stream, and most nodes
should auto-upgrade to it in the next few days.

However, some nodes may not be able to automatically upgrade due to
non-working rpm-ostreed.

Nodes that are stuck require manually intervention to proceed with
upgrades. The workaround is to manually mount /boot, restart rpm-ostree
and zincati, and let the auto-upgrades proceed:

```
sudo mount /dev/disk/by-label/boot /boot
sudo systemctl reset-failed rpm-ostreed.service
sudo systemctl restart rpm-ostreed.service zincati.service
```

Ciao, Luca