HPCC-8753 Reset persist calculation when re-executing a workflow item

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #3938 from ghalliday/issue8753

HPCC-8753 Reset persist calculation when re-executing a workflow item

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>