iotests: 085: Avoid image locking conflict

In the case where we test the expected error when a blockdev-snapshot
target already has a backing image, the backing chain is opened multiple
times. This will be a problem when we use image locking, so use a
different backing file that is not already open.

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2 files changed