parallels: Use generic infrastructure for BAT writing in parallels_co_check()

parallels: Use generic infrastructure for BAT writing in parallels_co_check()

BAT is written in the context of conventional operations over the image
inside bdrv_co_flush() when it calls parallels_co_flush_to_os() callback.
Thus we should not modify BAT array directly, but call
parallels_set_bat_entry() helper and bdrv_co_flush() further on. After
that there is no need to manually write BAT and track its modification.

This makes code more generic and allows to split parallels_set_bat_entry()
for independent pieces.

Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Message-Id: <20230424093147.197643-6-alexander.ivanov@virtuozzo.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>