HPCC-11905 Regression test engine sensitive to parameter order

Restructure parmater handling code.

Update README.rst

Signed-off-by: Attila.Vamos <attila.vamos@gmail.com>
Merge pull request #6608 from AttilaVamos/HPCC-11905-fix

HPCC-11905 Regression test engine sensitive to parameter order

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>