Update to make temp dir and python3 path a bit more OS agnostic

[dmoore44]

• Made temp file location OS independent - temp files were originally saved to /tmp, but this doesn't work so well if ViperMonkey is installed to FLARE VM.
• Added a check for python3 binary location, just in case python3 was installed using the command alias "python" rather than "python3" as was the case in my FLARE VM. This is a bit janky and could probably benefit from a better coder cleaning it up.