Drop flake8 2.1.0

Complete the move to flake8 2.2.2

Change-Id: Ib3a202aadb979af449dbee3f99d04beda5f6e3e2
Update retrying to 1.2.2

Version 1.2.2 contains an important bug fix to not raise a RetryError
exception on failure when exceptions aren't being wrapped.

Change-Id: I5203bf833fd015e87245661262b91ff8d0badba5
Merge "Update retrying to 1.2.2"
Merge "Drop flake8 2.1.0"