LU-5322 libcfs: handle vfs_rename change in 3.15+ kernels

LU-5322 libcfs: handle vfs_rename change in 3.15+ kernels

Starting with 3.15 kernels vfs_rename takes 6 arguments.
This patch adds support for this change.

Change-Id: I64ac982a3d7be03c61005fc899786b710f2fde57
Signed-off-by: James Simmons <uja.ornl@gmail.com>
Reviewed-on: http://review.whamcloud.com/11058
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>