Run hacking and flake checks for real

Previous tox configuration didn't run any of hacking or flake8 checks. This
commit enables both. Here are details:
* Added hacking to test-requirements. It'll manage it's own dependencies -
  pep8, pyflakes, and flake8
* Enabled flake8
* Disabled a bunch of hacking and flake rules. They should be fixed in next
  dependend patches
* Add noqa where necessary
* Fix H902 Use the 'not in' operator for collection membership evaluation

Change-Id: If8b05ed64b028a128ebcd78722e57cb9023928a4
Merge "Run hacking and flake checks for real"