LU-14781 osp: osp_object_free access NULL pointer

LU-14781 osp: osp_object_free access NULL pointer

If a osp_object is created by multiple threads at the same time,
lu_object_find_at() could allocate an osp_object without object
initialization, before hash inserting of the object, it find another
object has been created and inserted by another thread, it will free
the unintialized osp_object, and osp_object_free() will access
an uninitialized list_head (opo_xattr_list).

This patch initialize osp_object::opo_xattr_list in its allocation
function.

Call trace:
            lu_object_free.isra.30+0xf2/0x170 [obdclass]
            lu_object_find_at+0x496/0x930 [obdclass]
            lod_initialize_objects+0x3e4/0xba0 [lod]
            lod_parse_striping+0x693/0xc20 [lod]
            lod_striping_load+0x2b2/0x660 [lod]
            lod_declare_destroy+0x12b/0x600 [lod]
            mdd_declare_finish_unlink+0x91/0x210 [mdd]
            mdd_unlink+0x48f/0xab0 [mdd]
            mdt_reint_unlink+0xc32/0x1550 [mdt]
            mdt_reint_rec+0x83/0x210 [mdt]
            mdt_reint_internal+0x6e1/0xb00 [mdt]
            mdt_reint+0x67/0x140 [mdt]
            tgt_request_handle+0xaee/0x15f0 [ptlrpc]
            ptlrpc_server_handle_request+0x24b/0xab0 [ptlrpc]
            ptlrpc_main+0xb34/0x1470 [ptlrpc]
            kthread+0xd1/0xe0

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: Ib86aca5b41e94a1758f177655ea3a0f680335e0f
Reviewed-on: https://review.whamcloud.com/45442
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>