Add inventory builder python script

Includes tox support for running unit tests.
Small note added to getting-started guide for using
inventory_builder.py

Also adds manual-only unit test.

contrib/inventory_builder/tox.ini

@@ -0,0 +1,28 @@
+[tox]
+minversion = 1.6
+skipsdist = True
+envlist = pep8, py27
+
+[testenv]
+whitelist_externals = py.test
+usedevelop = True
+deps =
+    -r{toxinidir}/requirements.txt
+    -r{toxinidir}/test-requirements.txt
+setenv = VIRTUAL_ENV={envdir}
+passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
+commands = py.test -vv #{posargs:./tests}
+
+[testenv:pep8]
+usedevelop = False
+whitelist_externals = bash
+commands =
+    bash -c "find {toxinidir}/* -type f -name '*.py' -print0 | xargs -0 flake8"
+
+[testenv:venv]
+commands = {posargs}
+
+[flake8]
+show-source = true
+builtins = _
+exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg