LU-2904 llite: return valid fsid for statfs

Lustre uses 64-bits inode number to identify object on client side.
When re-export Lustre via NFS, NFS will detect whether support fsid
via statfs(). For the non-support case, it will only recognizes and
packs low 32-bits inode number in nfs handle. Such handle cannot be
used to locate the object properly.

To avoid patch linux kernel, Lustre client should generate fsid and
return it via statfs() to up layer.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Ie292b26726a1b2aa7a763ef7c0507e3ed089323b
Reviewed-on: http://review.whamcloud.com/6493
Tested-by: Hudson
Tested-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>