Yzl/rpm packager

:construction: 

@opscode/release-engineers This code is working minimally, but it's extremely unattractive and I could use some feedback on how to organize and rewrite it to be less painful.  In particular, things that are bothering me are

- how to organize for readability and testing
- naming things is hard
- a lot of the code for copying an install to staging/build areas is copy-pasta from fpm; can we replace with straight copies/syncs because the use case we want to support is much less complex? 


This is making paths relative? We should use this instead:

```ruby
Pathname.new(p).relative_path_from(Pathname.new(staging_path))
```