Inc_backup: add datastore element test scenarios to incremental backup

[meinaLi]

This update is coming from disk datastore new feature(RHEL-69449).

[meinaLi]

# avocado run --vt-type libvirt --vt-machine-type q35 incremental_backup.push_mode.original_disk_local
JOB ID     : 6d202e4580cda7135015cc6d89809cfd5c8e591b
JOB LOG    : /var/log/avocado/job-results/job-2025-01-14T03.47-6d202e4/job.log
 (01/44) type_specific.io-github-autotest-libvirt.incremental_backup.push_mode.original_disk_local.hotplug_disk.backup_to_qcow2.backup_to_file.reuse_target_file.negative_test.target_file_not_exist.without_datastore: STARTED
 (01/44) type_specific.io-github-autotest-libvirt.incremental_backup.push_mode.original_disk_local.hotplug_disk.backup_to_qcow2.backup_to_file.reuse_target_file.negative_test.target_file_not_exist.without_datastore: PASS (57.67 s)
……
 (44/44) type_specific.io-github-autotest-libvirt.incremental_backup.push_mode.original_disk_local.coldplug_disk.backup_to_raw.backup_to_block.positive_test.with_datastore: PASS (125.66 s)
RESULTS    : PASS 44 | ERROR 0 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 0 | CANCEL 0
JOB HTML   : /var/log/avocado/job-results/job-2025-01-14T03.47-6d202e4/results.html
JOB TIME   : 3737.11 s

# avocado run --vt-type libvirt --vt-machine-type q35 incremental_backup.pull_mode..with_datastore
JOB ID     : eb1b2d7f250a6220ffe7de298b809c62a455ed4d
JOB LOG    : /var/log/avocado/job-results/job-2025-01-14T05.38-eb1b2d7/job.log
 (01/22) type_specific.io-github-autotest-libvirt.incremental_backup.pull_mode.tls_disabled.original_disk_local.hotplug_disk.nbd_unix.scratch_to_file.reuse_scratch_file.negative_test.scratch_not_exist.default_exportbitmap.default_exportname.scratch_not_encrypted.with_datastore: STARTED
 (01/22) type_specific.io-github-autotest-libvirt.incremental_backup.pull_mode.tls_disabled.original_disk_local.hotplug_disk.nbd_unix.scratch_to_file.reuse_scratch_file.negative_test.scratch_not_exist.default_exportbitmap.default_exportname.scratch_not_encrypted.with_datastore: PASS (54.37 s)
……
(22/22) type_specific.io-github-autotest-libvirt.incremental_backup.pull_mode.tls_disabled.original_disk_local.coldplug_disk.nbd_tcp.scratch_to_block.positive_test.default_exportbitmap.default_exportname.scratch_not_encrypted.with_datastore: STARTED
 (22/22) type_specific.io-github-autotest-libvirt.incremental_backup.pull_mode.tls_disabled.original_disk_local.coldplug_disk.nbd_tcp.scratch_to_block.positive_test.default_exportbitmap.default_exportname.scratch_not_encrypted.with_datastore: PASS (111.96 s)
RESULTS    : PASS 22 | ERROR 0 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 0 | CANCEL 0
JOB HTML   : /var/log/avocado/job-results/job-2025-01-14T05.38-eb1b2d7/results.html
JOB TIME   : 2019.58 s