Format Python code following PEP-8 (plus other constraints)

[castarco]

In order to have a clear & consistent style for our Python code (mainly functional tests), we should enforce PEP-8, as it's a de-facto standard for the community.

Given that PEP-8 is far from being exhaustive, it would be convenient to add some extra formatting/style rules on top of it to improve style consistency.

We could use some tools to automate formatting and decrease our mental burden and spent time:

• AutoPEP: https://github.com/hhatto/autopep8
• YAPF: https://github.com/google/yapf
• Black: https://github.com/ambv/black

Expected benefits:

• We avoid sterile discussions on formatting.
• Merges and rebases become easier because style differences don't introduce unnecessary noise.

This "issue" is related to #60 .