radosgw-admin: adjust bucket link interface

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
Try a different approach to zombie prevention

The previous method I had committed had the unfortunate side-effect of
preventing teuthology job processes from giving their returncode to the
worker process. This method shouldn't do that.

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>