Fix comments and unittest for market.py and style

Trying to make the right commit to  the develop branch.
Logging is an implementation detail. You are welcome to assert that there is a `logger` attached to the object (like I do [here](https://github.com/OpenBazaar/OpenBazaar/blob/master/test/test_kbucket.py#L54)) but there is no reason to unit test the content that is logged. While we are at it, testing the output by user inspection (aka visually) does not qualify as a unit test, since it cannot be automated. Please do not interpret this comment as an invitatio