LU-2850 kernel: 3.8 upstream removes vmtruncate()

LU-2850 kernel: 3.8 upstream removes vmtruncate()

vmtruncate() is removed since upstream commit b9f61c3.
Also truncate_setsize is not always available. So we
just open code it and use truncate_pagecache instead.

Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: I9d4f43a5c181f16482b4caa021ba7a09ee52b600
Reviewed-on: http://review.whamcloud.com/5613
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Keith Mannthey <keith.mannthey@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>