ganeti cluster backend is IPv4-only
I tried to reboot the ganeti cluster yesterday and it failed with:
```
root@fsn-node-04.torproject.org: Permission denied (publickey).
```
weasel diagnosed this as:
```
16:57:08 <weasel> etc/ssh/userkeys/root only has v4 addresses in from=..
16:57:22 <weasel> that is probably a bug.
```
issue