LU-618 llite: IO accounting of page read

LU-618 llite: IO accounting of page read

When CONFIG_TASK_IO_ACCOUNTING is used with Lustre, writes are
accounted for but not read.

The accounting is normally done in the kernel for page writeback
and readahead functionlity, Therefore, as Lustre implements its
own readahead, it must also maintain its own accounting on read
(but not for write)

Change-Id: I19f330be65324a8da002f9d61cb9262345ecb012
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-on: https://review.whamcloud.com/1636
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>