console-conf should display information about broken seeds in case the system is broken

[Ian Johnson]

If one builds an Ubuntu Core image that eventually results in snapd failing to finish seeding, console-conf should detect this and show information about what happened/failed, as currently it is very hard to get this information if you are not skilled at hacking around things, and in the case of building a FDE enabled image, (hopefully) impossible to hack around to get information on what's broken.

Things that would be good to show a user when this happens:

* snapd logs from journald
* snap changes/tasks from /var/lib/snapd/state.json (if snapd the daemon is down, a nice version of this can be gotten via `snap debug state /var/lib/snapd/state.json)
* list of snaps in the seed (i.e. to get the version of the snaps)