Now that the Shipyard gates are running on Focal(20.04), flake8, grpcio,
and pyflakes need to use a version compatible with python3.8 and Ubuntu
20.04 which is the default python version in Ubuntu focal. Also unpinning
setuptools so that it is compatible with python3.8.
Additionally, address pep8 violations that arise from using a newer
version of flake8
Change-Id: Idc3c5d66b48fc9e4497a71d1b640bcd2872c22eb