Enable automatic validation of many HACKING rules.

 * Add hacking to the tox build - a set of flake8 plugins that
   perform automatic validation of many HACKING.rst rules.
 * This patch configures hacking in the tox build and performs
   the mechanical cleanup required to allow the checks to pass.
 * See https://pypi.python.org/pypi/hacking

Change-Id: Ib41313b5aae991e6ffef2a89dd69e83985bdc36d