LU-6389 llite: restart short read/write for normal IO

LU-6389 llite: restart short read/write for normal IO

If normal IO got short read/write, we'd restart the IO from where
we've accomplished until we meet EOF or error happens.

Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I4582affe8d2030df669b6e22b598b0c321e81466
Reviewed-on: http://review.whamcloud.com/14123
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>