HPCC-11614 Support outputting workunit result to disk in roxie

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6638 from ghalliday/issue11614

HPCC-11614 Support outputting workunit result to disk in roxie

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>