HPCC-10692 Allow options to be specified when running the regression suite

Add '-f...' parameter and handling code.

Overcome the python argparse library 'space in argument' handling problem.

Update '-X...' code to fix above problem

Update README.rst

Signed-off-by: Attila Vamos <attila.vamos@gmail.com>
Merge pull request #5988 from AttilaVamos/HPCC-10692-improvement

HPCC-10692 Allow options to be specified when running the regression suite

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>