LU-5707 lfsck: recreate LFSCK trace file for load failure

LU-5707 lfsck: recreate LFSCK trace file for load failure

The extended attribute XATTR_NAME_LFSCK_NAMESPACE for namespace
LFSCK trace file is enlarged since Lustre-2.7. When downgrade
from Lustre-2.7, the old MDS will get -ERANGE when loads the
XATTR_NAME_LFSCK_NAMESPACE extended attribute from the new
formatted on-disk namespace LFSCK trace file. Under such case,
the LFSCK should not return failure, instead, it can recreate the
XATTR_NAME_LFSCK_NAMESPACE EA as initialization case.

More further, if the LFSCK failed to load trace file, it is
unncessary to fail the whole LFSCK, instead, just recreate the
trace file.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Icc2c7087f9f4a20d57664eaaf5a92f6c6260c3aa
Reviewed-on: http://review.whamcloud.com/12278
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Patrick Farrell <paf@cray.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>