Refactor: python: Improve splitbraintest.py.

• Disable pylint warnings we can't really do anything about.

• Rename all methods to be private and follow python naming conventions.

• Use %r instead of repr in format strings.

• _isolate_partition and _heal_partition no longer return any value. It wasn't being used anywhere or even consistently returned.

• Simplify iterating over dicts by using values(), items(), or simply using "for x in xyz" as appropriate.

• Use the should_continue function.