qemu-iotests/197: use more generic commands for formats other than qcow2

In the previous commit e2f93826 ("tests/qemu-iotests/197: add
testcase for CoR with subclusters") we've introduced a new testcase for
copy-on-read with subclusters.  Test 197 always forces qcow2 as the top
image, but allows backing image to be in any format.  That last test
case didn't meet these requirements, so let's fix it by using more
generic "qemu-io -c map" command.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Message-ID: <20230907220718.983430-1-andrey.drobyshev@virtuozzo.com>
Tested-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>