run_qemu.sh: add autologin with shadow login (Ubuntu)

[marc-hb]

Note this still requires agetty > 2.39 and works only with Ubuntu 24.10 and above, see #169 for details.

[marc-hb]

Works for me on 24.10, @ikitayama can you try?

On Ubuntu 24.04 this saves only half the time: login is required but not the password.

[ikitayama]

@marc-hb I cherry-picked your commit, but I get still asked the password (Yes, I started with the script with the -r wipe option).

[marc-hb]

Do you get prompted only for the password, not the user account?

What is the output of the tty command after entering the password? If it's different from ttyS0, can you try to adjust the script in this PR? EDIT: I see ttyAMA0 in #140 (comment). EDIT2: I just de-hardcoded it a bit.

After login, can you check /etc/pam.d/login* and make sure they are as expected by this PR?

Finally, it would be great if you could run:

ssh rq
journalctl -f

... in another terminal and observe while entering your password on the serial terminal.

[marc-hb]

This has been working very well for me and at worst it made no difference to @ikitayama so I think this is OK to merge @stellarhopper

[stellarhopper]

Ah sorry, I wasn't sure if there was any testing pending. Looks good to me!