Upgrade to Omnibus 4.0

Before merging we'll ensure the following projects can be built:

* [x] ChefDK - http://manhattan.ci.opscode.us/job/chefdk-trigger-ad_hoc/281/downstreambuildview/
* [x] Chef 12 - http://ci.opscode.us/job/chef-client-build/1768/

This branch requires the following PRs also be merged:
https://github.com/opscode/omnibus/pull/338
https://github.com/opscode/omnibus-software/pull/297

I will update WIP commit 2e4925e after the above are merged.

should probably make it consistent and include it in the chef software defn outside of the windows? check as well then.