Expand image_check to all qemu-img checkable formats

and modify the qemu_storage.py to expand to support check qed qcow2v3
and fix a typo introduced by me in 651,
the "image_format" param should still be qcow2 for qcow2v3.
I was renaming the qcow3 to qcow2_v3 in 630, but I mistakenly set the branch to master when
opening the pullreq, then reopen it on 651 to branch next, but that time I mistakenly modified the 'image_format'

Signed-off-by: Xiaoqing Wei <xwei@redhat.com>