LU-14303 tests: parallel-scale test rr_alloc fails

LU-14303 tests: parallel-scale test rr_alloc fails

Correct the parameter for DNE environment. Else the
test case will fail on 'No such file or directory'.

Signed-off-by: Yang Sheng <ys@whamcloud.com>
Change-Id: Ib94c5b17a3b49153ac229bfc4dfcee39bd9f60d4
Reviewed-on: https://review.whamcloud.com/41192
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>