test/unit: fix all pep8 errors
test/unit: fix all pyflakes errors
tox.ini: run pep8/pyflakes on `test` package also

This is done so that we also ensure good style in our test code.
test/unit: better multiline string style
Merge pull request #88 from larsbutler/test-code-pep8-and-pyflakes

Fix pep8 and pyflakes errors in test code