iotests: Add test for data_off check

Write a pattern to the first cluster. Corrupt the data_off field and check
if the field was repaired on image opening and the pattern has not changed.

Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Denis V. Lunev <den@openvz.org>
2 files changed