HPCC-8901 Add priorityValue to the workunit information

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4050 from ghalliday/issue8901

HPCC-8901 Add priorityValue to the workunit information

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>