Add automatic python style checks

[bashir2]

trafficstars

As our Python code base is getting larger, we need an automatic way of checking style issues in our continuous build to avoid "style nit" comments in reviews. We should be able to set up and use pylint for this. As part of this, it is probably useful to enable some other static analysis that pylint offers.

[bashir2]

One option for code formatting is yapf.

[gdevanla]

We can use black instead. It gives consistent formatting given that it is opinionated.