LU-417 llite: report non-zero blocks on writing client

Writing client may not report accurate allocated block numbers when
dirty pages has not been writting back to OSTs, some "cp" or "tar" may
skip the file because it thinks it is completely sparse.

This patch makes writing client consider dirty pages when reporting
allocated blocks, lest the file be treated as a completely sparse one.

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I985d50a44ea1e917bf8e1cba3b5cb770eec35c3f
Reviewed-on: http://review.whamcloud.com/1647
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>