LU-3138 osd: ignore unlink inode in index delete

LU-3138 osd: ignore unlink inode in index delete

We should ignore unlink inode during index delete, otherwise
inode will be become bad inode, which cause unclean delete.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Ie3c99cd3bfa71876b34007bb5754360c73fc6f86
Reviewed-on: http://review.whamcloud.com/6072
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>