qemu-img: Report convert errors by bytes, not sectors

qemu-img: Report convert errors by bytes, not sectors

Various qemu-img commands are inconsistent on whether they report
status/errors in terms of bytes or sector offsets.  The latter is
confusing (especially as more places move to 4k block sizes), so let's
switch everything to just use bytes everywhere.  One iotest is
impacted.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20200402135717.476398-1-eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>