generic/098: update test for truncating a file into the middle of a hole

generic/098: update test for truncating a file into the middle of a hole

This updates generic/098 by adding a sync option, i.e. 'sync' after
the second write, and with btrfs's NO_HOLES, we could still get
wrong isize after remount.

This gets fixed by the patch

'Btrfs: fix truncate down when no_holes feature is enabled'

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>