Deprecate Ubuntu focal support

[likebreath]

Ubuntu focal has been end-of-life with its 5 years of standard security maintenance this month. This issue is to track the deprecation process of Ubuntu focal support with our repository, mainly about our documentation and integration tests.

[gjolly]

Noble (Ubuntu 24.04) is the latest LTS release and is probably what should be used.

I think the doc should point to the release images located under https://cloud-images.ubuntu.com/releases/ instead of the daily images (see this doc for more details).

[tpressure]

I just found out that any Ubuntu cloud images fails to boot when following the official tutorial. See https://github.com/cloud-hypervisor/rust-hypervisor-firmware/issues/382

It works fine with EDK2 (CLOUDHV.fd) though.

[gjolly]

Focal is going to be EOSS in 7 days. If the firmware issue cannot be resolved by then, a good alternative could be to document downloading the unpacked kernel from https://cloud-images.ubuntu.com/releases/noble/release/unpacked/ubuntu-24.04-server-cloudimg-amd64-vmlinuz-generic to boot the image:

wget https://cloud-images.ubuntu.com/releases/noble/release/unpacked/ubuntu-24.04-server-cloudimg-amd64-vmlinuz-generic
wget https://cloud-images.ubuntu.com/releases/noble/release/ubuntu-24.04-server-cloudimg-amd64.img
qemu-img convert -p -f qcow2 -O raw ubuntu-24.04-server-cloudimg-amd64.img ubuntu-24.04-server-cloudimg-amd64.raw

cloud-hypervisor --serial tty --console off --cmdline 'console=ttyS0 root=/dev/vda1' \
        --kernel ubuntu-24.04-server-cloudimg-amd64-vmlinuz-generic \
        --disk path=ubuntu-24.04-server-cloudimg-amd64.raw path=/tmp/cloud-init.img \
        --cpus boot=4 \
        --net "tap=tap0" \
        --memory size=1G

In fact, we don't even need an initramfs because the generic kernel has all the necessary virtio drivers built-in.