its-migrate-unmapped-collection on X-AWS-4.15 a1.metal timeout with Ncat: Connection refused.

[Po-Hsu Lin]

Issue found on X-AWS 4.15.0-1119.126~16.04.2 with ARM64 node a1.metal

I don't think this is a regression as this test seems never finished properly on this node with previous kernels:
  * 4.15.0-1118.125~16.04.1 - deployment failed
  * 4.15.0-1116.123~16.04.1 - test incomplete, probably test killed with timeout
  * 4.15.0-1115.122~16.04.1 - test incomplete, probably test killed with timeout
  * 4.15.0-1113.120~16.04.1 - deployment failed
  * 4.15.0-1112.119~16.04.1 - deployment failed
  * 4.15.0-1111.118~16.04.1 - test incomplete, probably test killed with timeout

Test log:
ubuntu_kvm_unit_tests.its-migrate-unmapped-collection ubuntu_kvm_unit_tests.its-migrate-unmapped-collection timestamp=1643276759 timeout=1800 localtime=Jan 27 09:45:59
 Persistent state client._record_indent now set to 2
 Persistent state client.unexpected_reboot now set to ('ubuntu_kvm_unit_tests.its-migrate-unmapped-collection', 'ubuntu_kvm_unit_tests.its-migrate-unmapped-collection')
 Waiting for pid 13791 for 1800 seconds
 Running 'kvm-ok'
 INFO: /dev/kvm exists
 KVM acceleration can be used
'/home/ubuntu/autotest/client/tmp/ubuntu_kvm_unit_tests/src/kvm-unit-tests/tests/its-migrate-unmapped-collection'
 BUILD_HEAD=16647354
 run_migration timeout -k 1s --foreground 90s /usr/bin/qemu-system-aarch64 -nodefaults -machine virt,gic-version=host,accel=kvm -cpu host -device virtio-serial-device -device virtconsole,chardev=ctd -chardev testdev,id=ctd -device pci-testdev -display none -serial stdio -kernel /tmp/tmp.6fHs4DWDTB -smp 16 -machine gic-version=3 -append its-migrate-unmapped-collection # -initrd /tmp/tmp.Uq8EztBRs2
 SKIP: gicv3: its-migrate-unmapped-collection: No ITS, skip ...
 Now migrate the VM, then press a key to continue...
 qemu-system-aarch64: terminating on signal 15 from pid 14157
 qemu-system-aarch64: terminating on signal 15 from pid 14165
 Ncat: Connection refused.
 Ncat: Connection refused.
 Ncat: Connection refused.
 Ncat: Connection refused.