Update AthOptionsParser.py - pass argparsing onto script if doing `--help`...

Update AthOptionsParser.py - pass argparsing onto script if doing --help option and a script is provided

This MR was triggered by me noticing that if I do:

athena MyScript.py --help

I get the athena command's help messaging, rather than the MyScript.py's help messaging, which feels inconsistent with the fact that:

athena MyScript.py --opt1 --opt2 ...

Sees the options all passed onto the argparser defined in MyScript.py