Update performance script to python 3, and minor corrections

[mark-petersen]

Minor script updates. With these changes, the script produces performance scaling plots correctly.

[mark-petersen]

In a run directory, the command

./performance_test.py 1024 32 grizzly 36 EC60to30

produces this plot:

[xylar]

@mark-petersen, if you want to make the one suggested change above, I'll approve by inspection. If you would like me to test, please let me know what typical usage looks like.

[xylar]

@mark-petersen, based on your typical usage above (our messages crossed!), would you be willing to add argparse to this script so the arguments are named, rather than ordered and so there's help when you do ./performance_test.py --help.

Should we add this to the conda package?

[xylar]

If the answer is no to all of the above, that's fine.

[mark-petersen]

@xylar I agree about argparse. I had thought of that too. If you approve I'll merge this in now so students can use it, and argparse is a good exercise for a student to update.

[mark-petersen]

@xylar no need to test, visual inspection is fine.