[BLOCK] update IDE to use new blk_ordered for barriers

Update IDE to use new blk_ordered.  This change makes the
following behavior changes.

* Partial completion of the barrier request is handled as
  failure of the whole ordered sequence.  No more partial
  completion for barrier requests.

* Any failure of pre or post flush request results in failure
  of the whole ordered sequence.

So, successfully completed ordered sequence guarantees that
all requests prior to the barrier made to physical medium and,
then, the while barrier request made to the physical medium.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jens Axboe <axboe@suse.de>