Use version 3 of the yum cookbook

The 3rd verison of the yum cookbook introduces breaking changes,
so all cookbooks that use it need to be modified.
* Remove uses and tests for yum_key resource.
* Add gpgkey arg to yum_repository resource.
* Removed custom spec matchers as these are now provided by the yum cookbook.

blueprint yum-cookbook-v3-support

Change-Id: I1ce649b92fbd39010d88048ee2daf317425f0374
Upgrade/Update rubocop

Now that almost all of the rubocop blueprints have been completed, make
one final pass through all of the cookbooks ensuring they're all in
sync with each other.

- Upgrade rubocop to 0.18.1
- Fix violations caused by 0.18.1 upgrade
- Move Excludes for non-existent folders to Includes so they
  automatically cover future additions

Change-Id: Id66903d1ca0f5fc0fa3323cca2ec6880730db3fe
Implements: blueprint lint-and-unit-testing-for-havana
Merge "Upgrade/Update rubocop"