docs: fix Firecracker version and rootfs

[pb8o]

During the last change we missed updating the Firecracker CI version.

Also keep the rootfs as ext4 for the rest of the guide.

Fixes: a69595f

Changes

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Reason

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PR Checklist

• I have read and understand CONTRIBUTING.md.
• I have run tools/devtool checkstyle to verify that the PR passes the
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• I have described what is done in these changes, why they are needed, and
  how they are solving the problem in a clear and encompassing way.
• I have updated any relevant documentation (both in code and in the docs)
  in the PR.
• I have mentioned all user-facing changes in CHANGELOG.md.
• If a specific issue led to this PR, this PR closes the issue.
• When making API changes, I have followed the
  Runbook for Firecracker API changes.
• I have tested all new and changed functionalities in unit tests and/or
  integration tests.
• I have linked an issue to every new TODO.

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• This functionality cannot be added in rust-vmm.

[roypat]

The ext4 stuff works for me now, but the SSH commands at the end seem broken. It promps me for a password:

roypat@ua2d7e1a6107c5b:~/test$ ssh -i ./ubuntu-24.04.id_rsa [email protected]
[email protected]'s password: 

[pb8o]

The ext4 stuff works for me now, but the SSH commands at the end seem broken. It promps me for a password:

roypat@ua2d7e1a6107c5b:~/test$ ssh -i ./ubuntu-24.04.id_rsa [email protected]
[email protected]'s password: 

I see. The issue is the owner of files in the rootfs is not root. Should be fixed in the latest revision.

[Silvanoc]

The ext4 stuff works for me now, but the SSH commands at the end seem broken. It promps me for a password:

roypat@ua2d7e1a6107c5b:~/test$ ssh -i ./ubuntu-24.04.id_rsa [email protected]
[email protected]'s password: 

I see. The issue is the owner of files in the rootfs is not root. Should be fixed in the latest revision.

The last version works! Therefore LGTM

But is laying around a directory tree fully owned by root. That might be confusing for some users. Unfortunately I haven't found any solution that does not make the process more complex (like a disk image file).

[roypat]

Works now, thanks a bunch, Pablo!