LU-3348 test: use correct old path in racer's file_link.sh

LU-3348 test: use correct old path in racer's file_link.sh

In racer's file_link.sh the old path was not prefixed by the directory
used by racer. Since file_link.sh does not run out of this directory
no links were created. Fix this in by supplying the correct old path.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Ifcbcc3d50c70faed7a99fa95217b08c8efe35791
Reviewed-on: http://review.whamcloud.com/6351
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>