Format the code following PEP8.

This patch modifies the code to follow [PEP8](http://legacy.python.org/dev/peps/pep-0008/).

Change-Id: I9a916ce3909cfa6924cbd854e25b4c9a884c8960
Signed-off-by: Taku Fukushima <tfukushima@midokura.com>