LU-745 kernel: ost-pools test_23 hung

LU-745 kernel: ost-pools test_23 hung

It might be caused by a jbd2 bug which result in forever sleep
in the do_get_write_access().
http://www.spinics.net/lists/linux-ext4/msg24689.html

Apply the fix from Jan Kara to see if it can resolve the problem.

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I5dc74ab9fc49686fce9fdcff3c94ef8f0c35b38f
Reviewed-on: http://review.whamcloud.com/1541
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>