Improvement - Update gateway code from python 2 to python 3

Python 2 is no longer supported, we should migrate to python 3.

Python 2 was officially sunset on Jan 1, 2020: https://www.python.org/doc/sunset-python-2/

Prior to doing this, it would be helpful to reformat some of the code - there’s a mix of tabs and spaces (switch to only using spaces)

There’s a python tool called 2to3 that should help with this conversion. Here's a really simple example. Consider an old python2 file below - where there is a print statement without parenthesis:

cat old.py
print "hello, world"

We can run `2to3` on the file with the `-w` flag to edit it inline:

$ 2to3 -w old.py
RefactoringTool: Skipping optional fixer: buffer
RefactoringTool: Skipping optional fixer: idioms
RefactoringTool: Skipping optional fixer: set_literal
RefactoringTool: Skipping optional fixer: ws_comma
RefactoringTool: Refactored old.py
--- old.py	(original)
+++ old.py	(refactored)
@@ -1 +1 @@
-print "hello world"
+print("hello world")

You can see the print function was modified to convert it to something that's acceptable in python3.

1. Cleanup some of the indentation in the code - there mixed tabs and spaces all over the place, this should be converted to use spaces. This is used by the official python style guide.
2. Cleanup the python3 files
3. Make sure that the integration test runs properly