backingchain: add case for blockcopy with different qcow2 properities

[nanli1]

VIRT-294532: Check qcow2 properties after blockcopy

Signed-off-by: nanli [email protected]

Test result:

/usr/local/bin/avocado run --vt-type libvirt --test-runner=runner --vt-machine-type q35 backingchain.blockcopy.image_properties
JOB LOG    : /var/lib/avocado/job-results/job-2022-11-21T21.04-9076fbe/job.log
 (1/2) type_specific.io-github-autotest-libvirt.backingchain.blockcopy.image_properties.not_encrypt_disk.extended_l2_and_cluster_size: PASS (65.97 s)
 (2/2) type_specific.io-github-autotest-libvirt.backingchain.blockcopy.image_properties.encrypt_disk.extended_l2_and_cluster_size: PASS (62.87 s)