Refactoring of the #update_from_source method calls

I noticed a lot of repetition inside `fedora_rpm.rb` and thought I'd take a crack at refactoring it.

 - added tests to ensure the behaviour of each individual `update_foo` method remains consistent
 - added a test around `update_from_source` to ensure all the `update_foo` methods are called
 - extracted the common behaviour from each individual `update_foo` method to a private `yield_and_update` method which yields the specific behaviour