LU-2449 osd: osd-zfs to initialize parent attribute

LU-2449 osd: osd-zfs to initialize parent attribute

to follow ZFS on-disk format osd_object_create() should
initialize regular attribute storing parent dnode.
parent dnode is taken from object passed to create as an
allocation hint.

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: I1b4b4b5d7c6989c39f6bdecd52af48f270ad5beb
Reviewed-on: http://review.whamcloud.com/5642
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>