This patch updates our hacking checks as follows:
- Hacking checks are now registered via entry points so
they can be used via flake8 CLI. By default they are disabled.
Hacking check doc string is also updated to support pep8
parsing of check code.
- The existing hacking.checks.factory() is moved to a more
meaningful name; marking as deprecated.
- A private neutron-lib specific hacking check factory is provided
and used in tox.ini.
- A flake8 plugin is provided that supports the ability to use our
hacking check factory functions to enable a pre-existing check
by default.
- Our usage of hacking checks is updated to reflect our consumption
model for adopters.
- Unit tests are provided.
Change-Id: I88dad7f7cce4d4f5af679272f067c3bb4a73803a
4f318bc253