Handle fsck failures gracefully

Fsck failure can cause the system to drop the user into the emergency shell. Example while testing:

[FAILED] Failed to start File System Check o…03f04-af81-46c6-817c-e788adfa1d51.
See 'systemctl status "systemd-fsck@dev…\x2de788adfa1d51.service"' for details.
[DEPEND] Dependency failed for /boot.
[DEPEND] Dependency failed for Local File Systems.
[  OK  ] Reached target Sound Card.
[...]
[  OK  ] Reached target Network.
You are in emergency mode. After logging in, type "journalctl -xb" to view
system logs, "systemcGive root password for maintenance
(or press Control-D to continue):

This needs to be handled gracefully on the phone, either by:

• giving the user some sort of a touch-based shell, or
• trying to repair (except for a data partition?), or
• restoring some known working image, or
• noisily telling the user to find a keyboard and deal with it