Support files for unit test of software-config hooks

This change adds a tox.ini file including environments
for py26, py27 and pep8. These will be used to unit test the
hot software-config hooks.

Change-Id: Ieea12be77205d777a6b9c0f1c239418b9ce59d9f
Unit test of 55-heat-config

This implements a unit test of the os-refresh-config script 55-heat-config.

The test does the following:
- hook-fake.py is a fake hook which is executed for every config item
  found by 55-heat-config
- test_heat_config.HeatConfigTest does the following:
  - creates a temp dir and copies hook-fake.py into it for every
    hook/group name the test expects (puppet, script etc)
  - writes our sample config json and invokes 55-heat-config
    to trigger the execution of the fake hook for each config item
  - assert that the fake hooks wrote out the expected json for each
    config item

Change-Id: I87c108dc07dacde767b7f74c82c7ae06ab765738
flake8 fixes for software-config hooks

Fixed as raised by tox -epep8

Change-Id: I58412f82283e4aba1236e4cf7044ef6fd73400a9