Refactor to server-specific configuration. Generate Postgres password on the fly.
Fix postgres password generation
Only do password lookup once, relative to `inventory_dir` (which is where the `hosts` file is kept, e.g. the root of this repo)
Start nginx at the end of nginx-passenger role
Merge branch 'server-specific-config'

* Refactor things that don't apply to the global nginx installation out into their own roles.