deprecate existed rbd image

[nanli1]

create rbd image for backingchain case instead of using existed rbd image

Signed-off-by: nanli [email protected]

Test result:

relative path case

avocado run --vt-type libvirt --test-runner=runner --vt-machine-type q35 backingchain.blockcommit.relative_path  --vt-connect-uri qemu:///system
 (1/8) type_specific.io-github-autotest-libvirt.backingchain.blockcommit.relative_path.file_disk.keep_relative.active.vm_started: PASS (40.36 s)
 (2/8) type_specific.io-github-autotest-libvirt.backingchain.blockcommit.relative_path.file_disk.keep_relative.active.vm_paused: PASS (42.28 s)
 (3/8) type_specific.io-github-autotest-libvirt.backingchain.blockcommit.relative_path.file_disk.keep_relative.inactive.vm_started: PASS (41.35 s)
 (4/8) type_specific.io-github-autotest-libvirt.backingchain.blockcommit.relative_path.file_disk.keep_relative.inactive.vm_paused: PASS (40.81 s)
 (5/8) type_specific.io-github-autotest-libvirt.backingchain.blockcommit.relative_path.block_disk.keep_relative.active.vm_started: PASS (80.68 s)
 (6/8) type_specific.io-github-autotest-libvirt.backingchain.blockcommit.relative_path.block_disk.keep_relative.active.vm_paused: PASS (81.71 s)
 (7/8) type_specific.io-github-autotest-libvirt.backingchain.blockcommit.relative_path.rbd_with_auth_disk.keep_relative.active.vm_started: PASS (51.21 s)
 (8/8) type_specific.io-github-autotest-libvirt.backingchain.blockcommit.relative_path.rbd_with_auth_disk.keep_relative.active.vm_paused: PASS (42.25 s)

avocado run --vt-type libvirt --test-runner=runner --vt-machine-type q35 backingchain.blockpull.relative_path  --vt-connect-uri qemu:///system
 (1/3) type_specific.io-github-autotest-libvirt.backingchain.blockpull.relative_path.file_disk.keep_relative: PASS (39.73 s)
 (2/3) type_specific.io-github-autotest-libvirt.backingchain.blockpull.relative_path.block_disk.keep_relative: PASS (81.10 s)
 (3/3) type_specific.io-github-autotest-libvirt.backingchain.blockpull.relative_path.rbd_with_auth_disk.keep_relative: PASS (41.35 s)
RESULTS    : PASS 3 | ERROR 0 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 0 | CANCEL 0