add very basic ch-remote live-migration test

[phip1611]

It not necessarily belongs to libvirt-tests but we can't use the CHV upstream integration test infrastructure for reasons. Might be worth it to have at least a stripped down live-migration test based on ch-remote in our pipeline here.

These are roughly the commands you need (this is what I use for local development)

• CHV 1:
  reset; rm -f /tmp/chv1.sock && cargo run --release --bin cloud-hypervisor -- --api-socket /tmp/chv1.sock --kernel ./linux_6_12.bzImage --cmdline "console=ttyS0" --serial tty --console off --initramfs ./initrd --seccomp log -vv --memory size=8G --cpus boot=8
• CHV 2:
  reset; rm -f /tmp/chv2.sock; cargo run --release --bin cloud-hypervisor -- --api-socket=/tmp/chv2.sock
• ch-remote 1:
  cargo run --bin ch-remote -- --api-socket=/tmp/chv1.sock send-migration tcp:127.0.0.1:1337 --downtime 200 --migration-timeout 12000
• ch-remote 2:
  cargo run --bin ch-remote -- --api-socket /tmp/chv2.sock receive-migration tcp:127.0.0.1:1337