python: Resolve some indentation warnings.

python: Resolve some indentation warnings.

This patch resolves the following warnings from flake8:

 E111 indentation is not a multiple of four
 E112 expected an indented block
 E113 unexpected indentation

It's critical to have correct indentation in Python code, so it seemed
worth enabling these warnings.

Signed-off-by: Russell Bryant <russell@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>