Add pydocstyle tool to Review Bot

Review Request #10197 — Created Oct. 4, 2018 and submitted — Latest diff uploaded




Users can now configure Review Bot to run pydocstyle, a tool for checking
compliance with Python docstring conventions.

Pydocstyle is not added to the install requires list and users will
need to manually install it to use it.

Pydocstyle defaults to using the PEP 257 docstring convention but users
can add a list of errors to ignore which will override the convention.

Tested dependency check by running reviewbot worker command without
pydocstyle installed

Tested pydocstyle by adding new configuration to Review Bot integration
and publishing a review. Also tested with errors added to ignore list.