LU-8159 osd-ldiskfs: cache xattr in osd-ldiskfs

LU-8159 osd-ldiskfs: cache xattr in osd-ldiskfs

In LU-7660 LOD doesn't cache default striping, so each create will
get it from bottom. LU-7660 has enabled xattr cache in OSP, and
osd-zfs caches xattr already, this patch introduces a similar
mechanism in osd-ldiskfs.

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Change-Id: I3382119acaf9a819ee2be9737d1eae833e9ea2a4
Reviewed-on: http://review.whamcloud.com/20496
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>