Load default config in `PlotlyTestCase`.
Load default config in `PlotlyTestCase`.

Clean-slates each test. It doesn’t mean that the files aren’t dirty
between tests, but because `session` takes precedence, this helps a lot.

plotly/plotly.py,plotly/python-api,plotly/plotly.py,plotly/plotly.py,plotly/python-api,plotly/python-api