Reformat generate_data.py using yapf and add extra lines.
Reformat generate_data.py using yapf and add extra lines.

We are currently using yapf to format python files. However, some lines
are strange and difficult to read. Thus, we added some extra lines
between chunks of code to make it easier to read.

googleinterns/av1-codec-comparison,googleinterns/av1-codec-comparison,googleinterns/av1-codec-comparison