Setting up a base new-relic setup using ansible vault

- Fixes #67 

- [x] Document `vars.yml` and `secrets.yml` and `secrets.vault.yml`
- [x] make ansible not crash with log permissions

This change also introduces a new `ansible-vault` secrets file, which has our encrypted `new-relic` key. A side-effect of this now you'll always need the vault key to deploy/setup.

Thoughts?
Looks like this file still references the unencrypted `secrets.yml`. It also *doesn't* reference `vars.yml`; bug or by design?