not able to SSH access a server after bridge-utils was removed

[Patricia Domingues]

I've upgraded a server via `do-release-upgrade` from Ubuntu Bionic to
Focal. It was ENI configured (since Ubuntu 12.04 Precise):

```
auto lo
iface lo inet loopback

# The primary network interface
iface eth0 inet manual

# The primary bridge interface
auto br0
iface br0 inet static
 address 10.230.71.10
 netmask 255.255.248.0
 gateway 10.230.64.1
 bridge_ports eth0
 dns-nameservers 10.230.64.1
```

and I lost SSH access to the system after the upgrade was completed because bridge-utils was removed during the last upgrade phase:

```Remove obsolete packages?
187 packages are going to be removed.
...
Removing bridge-utils (1.6-2ubuntu1) ...
```
I think the reason was because `bridge-utils` was automatically installed, probably via `libvirt-bin`, but is this correct - a automatically package cleanup happening in an "obsolete removal" phase?

[Patricia Domingues (patriciasd)]

I know it could be a special case where bridge-utils was not manually installed and you are still using ENI instead of netplan, but other people may hit the same problem