HPCC-10013 - Correct usage syntax of listworkunits

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #4821 from jakesmith/hpcc-10013

HPCC-10013 - Correct usage syntax of listworkunits

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>