Refactor "global attributes" into library methods

This has several benefits:

  + The attributes file is no longer crowded with attributes that are
    not configurable anyway.
  + We can add tests on library methods.
  + It just makes more sense!

Another change to be mindful of is that since services are no longer
represented as attributes, we don't have to make a copy (we create a
new instance every time we call enabled_services), and we no longer
have to convert to a hash (since we're already getting a hash).
Remove useless include_attribute
Add option to skip build packages in release
Release: 7.9.0
Merge pull request #100 from Scalr/release-7.9.0

Release 7.9.0