HPCC-8237 Add options to stress test callback usage in roxiemem

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4507 from ghalliday/issue8237

HPCC-8237 Add options to stress test callback usage in roxiemem

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>