Add a Chef::Audit::Controls object to help with namespacing

This solves two of the problems we are currently seeing:

1. RSpec configuration shared by audits and our own spec tests cause undesired behavior when running `rspec`,
2. Serverspec types interfere with Chef DSL (e.g., `package`).

\cc @tyler-ball @sersut 
@danielsdeleo I am curious about your thoughts on this?