parallels: Add data_start field to BDRVParallelsState

In the next patch we will need the offset of the data area for host cluster
index calculation. Add this field and setting up code.

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