LU-6218 osd-zfs: increase redundancy for meta data

LU-6218 osd-zfs: increase redundancy for meta data

Use DMU_OTN_UINT8_METADATA for local objects so their
data blocks would get an additional ditto copy. This
increases redundancy and hence the chance of recovery
by zpool scrub in the event of corruption.

Change-Id: I502da680521027733ea53744905c47f569a1b531
Signed-off-by: Isaac Huang <he.huang@intel.com>
Test-Parameters: mdtfilesystemtype=zfs mdsfilesystemtype=zfs ostfilesystemtype=zfs
Reviewed-on: http://review.whamcloud.com/13741
Tested-by: Jenkins
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>