Fix change media update device failure

[chunfuwen]

Fix change media update device failure
This may happen in case VM is not real ready to update device

[chunfuwen]

cleaning libvirtd logs...
DATA (filename=output.expected) => NOT FOUND (data sources: variant, test, file)
DATA (filename=stdout.expected) => NOT FOUND (data sources: variant, test, file)
DATA (filename=stderr.expected) => NOT FOUND (data sources: variant, test, file)
PASS 1-type_specific.io-github-autotest-libvirt.virsh.change_media.cdrom_test.scsi_.positive_test.update.block.running_guest

[chunfuwen]

previously failure log:

2024-09-09 08:47:02,483 stacktrace L0039 ERROR|
2024-09-09 08:47:02,483 stacktrace L0041 ERROR| Reproduced traceback from: /var/ci/libvirt-ci/runtest/avocado-vt/avocado-vt/avocado_vt/test.py:292
2024-09-09 08:47:02,486 stacktrace L0045 ERROR| Traceback (most recent call last):
2024-09-09 08:47:02,486 stacktrace L0045 ERROR| File "/var/lib/avocado/data/avocado-vt/virttest/test-providers.d/downloads/io-github-autotest-libvirt/libvirt/tests/src/virsh_cmd/domain/virsh_change_media.py", line 280, in run
2024-09-09 08:47:02,486 stacktrace L0045 ERROR| test.fail("Disk isn't a 'block' device")
2024-09-09 08:47:02,486 stacktrace L0045 ERROR| File "/var/ci/libvirt-ci/runtest/avocado-vt/avocado/avocado/core/test.py", line 979, in fail
2024-09-09 08:47:02,486 stacktrace L0045 ERROR| raise exceptions.TestFail(message)
2024-09-09 08:47:02,486 stacktrace L0045 ERROR| avocado.core.exceptions.TestFail: Disk isn't a 'block' device