LU-8454 llite: normal user can't set FS default stripe

Current client doesn't check permission before updating filesystem
default stripe on MGS, which isn't secure and obvious.

Since we setattr on MDS first, and then set default stripe on MGS,
we can just return error upon setattr failure.

Now filesystem default stripe is stored in ROOT in MDT, so saving
it in system config is for compatibility with old servers, this
will be removed in the future.

Add sanity 65m to verify this.

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Change-Id: Ia224a9211c1ceab08a3a064adc67bc945ee3fc11
Reviewed-on: http://review.whamcloud.com/21612
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>