ZTS: Fix zpool_import_hostid_changed_unclean_export

[behlendorf]

Motivation and Context

Apply the same fix from #16570 to this similar test case.

https://github.com/openzfs/zfs/actions/runs/11074121440/job/30772504124

   Test (Linux): /usr/share/zfs/zfs-tests/tests/functional/cli_root/zpool_import/zpool_import_hostid_changed_unclean_export (run as root) [00:00] [FAIL]
  21:53:15.14 SUCCESS: zgenhostid -f 01234567
  21:53:15.25 SUCCESS: zpool create testpool1 /var/tmp/dev_import-test/disk0
  21:53:15.27 SUCCESS: cp /var/tmp/dev_import-test/disk0 /var/tmp/dev_import-test/disk0.bak
  21:53:15.31 SUCCESS: zpool export testpool1
  21:53:15.32 SUCCESS: cp -f /var/tmp/dev_import-test/disk0.bak /var/tmp/dev_import-test/disk0
  21:53:15.32 SUCCESS: rm -f /var/tmp/dev_import-test/disk0.bak
  21:53:15.33 SUCCESS: zgenhostid -f 89abcdef
  21:53:15.36 SUCCESS: zpool import -d /var/tmp/dev_import-test testpool1 exited 1
  21:53:15.46 	Recovery is possible, but will result in some data loss.
  21:53:15.46 	Returning the pool to its state as of Fri Sep 27 21:53:15 2024
  21:53:15.46 	should correct the problem.  Recovery can be attempted
  21:53:15.46 	by executing 'zpool import -F testpool1'.  A scrub of the pool
  21:53:15.46 	is strongly recommended after recovery.
  21:53:15.46 cannot import 'testpool1': I/O error

Description

Update the test case to freeze the pool then export it to better simulate a hard failure. This is preferable to copying the vdev while the pool's imported since with a copy we're not guaranteed the on-disk state will be consistent. That can in turn result in a pool import failure and a spurious test failure.

How Has This Been Tested?

Will be tested by the CI, but the fix is identical to ab1b87e.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)