Give environment-specific overrides precedence
.env is now suitable for local development/testing

We ignore .env.test so that it doesn't require git gymnastics to add
secret keys in tests without accidentally committing them to the repo.
Now that the Supermarket cookbook overwrites .env, we don't have to
worry so much about what's in it.
Merge pull request #544 from opscode/dotenv-refinements

Dotenv refinements