refs #6667 modifying system tests to work with new dgreduce

in ISIS
refs #6667 Added dgreducer based system test for MAPS
refs #6667 minor changes

mainly related to ongoing work on other branches
refs #6667 MAPS system test modified to work hopefully right

and produce correct WB cross-section if set up this way (currently it is not and runs against some run data)
refs #6667 Modified MAPS and MARI System tests pass

one more workflow test has been added for MARI
refs #6667 System tests modified to work for dgreduce.
Merge branch 'feature/6667_ISISReductionInMantid' into develop