iotests: Use _img_info in test 089

iotests: Use _img_info in test 089

Currently, test 089 uses $QEMU_IMG info manually in order to obtain the
according output. However, the iotests should generally use _img_info as
this filters out more irrelevant information such as the host image size
or format specific information. Therefore, test 089 should use _img_info
as well.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reported-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>