fix(urunc-deploy): use the host architecture for the QEMU path in config.toml

[aman21-droid]

Description

On arm64 nodes urunc-deploy installed the QEMU binary as qemu-system-aarch64 but wrote
qemu-system-x86_64 into /etc/urunc/config.toml, so QEMU backed containers could not start.
install_artifacts uses qemu-system-$(uname -m) while the path in config.toml was fixed to
x86_64, and install_urunc_config copied that file to the host unchanged.

config.toml now carries a @QEMU_BINARY@ placeholder on the QEMU path line, and
install_urunc_config substitutes qemu-system-$(uname -m) as it copies the file.

Also adds deployment/urunc-deploy/config.toml to the paths: list in build-trigger.yml. The
Dockerfile COPYs that file into the image, but a change to it alone would not have triggered a
rebuild.

Related issues

• Fixes urunc-deploy writes an x86_64 QEMU path into config.toml, so QEMU containers fail on arm64 nodes #1003

How was this tested?

Ran the real install.sh against a reconstructed image layout with uname -m returning each
architecture:

• aarch64: installs qemu-system-aarch64, configures /opt/urunc/bin/qemu-system-aarch64
• x86_64: installs qemu-system-x86_64, configures /opt/urunc/bin/qemu-system-x86_64

The x86_64 output is byte identical to the config that shipped before this change, so there is no
behaviour change on amd64.

Fed the generated arm64 config to a locally built urunc and ran create/start on a qemu bundle. The
previous error is gone:

failed to apply rootfs mounts: failed to apply mount /opt/urunc/bin/qemu-system-x86_64:
failed to stat mount source /opt/urunc/bin/qemu-system-x86_64: no such file or directory

urunc now gets past the mount stage and reaches the monitor execve.

I do not have arm64 hardware, so the architecture-dependent half was exercised by controlling
uname -m rather than on a real arm64 node. The runtime half does not depend on host
architecture, it is a path that does not resolve.

LLM usage

Claude opus investigating the bug and fixes.

Checklist

• I have read the contribution guide.
• The linter passes locally (make lint).
• The e2e tests of at least one tool pass locally (make test_ctr, make test_nerdctl, make test_docker, make test_crictl).
• If LLMs were used: I have read the llm policy.

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[cmainas]

Hello @aman21-droid ,

thank you for the fix. Just one small comment.

[cmainas]

Thank you @aman21-droid for the quick fix. Please squash your commits so we can merge this.

[aman21-droid]

done

[aman21-droid]

@cmainas the CI runs are sitting in awaiting approval after the force-push —
could you hit 'Approve and run workflows' when you have a moment?