Add enable flag for RDO yum repository on RHEL

Each user can have their own specific repository for OpenStack.
Under this scenario, a flag is required to let user disable
the RDO yum repository.

Co-Authored-By: Matt Odden <mrodden@us.ibm.com>
Change-Id: Ifb271b5e11f3e26c5a217fcdd64ad546e378447f
Closes-Bug: #1269348
Rubocop cleanup - removing individual directory .rubocop.yml files

- Remove .rubocop.yml file from attributes directory.
- This is already managed by the single .rubocop.yml file ~/.rubocop.yml

Change-Id: Iee05b4f23d7fd20f45ad64f50b1f9eeb19c151f3
Addresses: blueprint rubocop-for-common
Merge "Add enable flag for RDO yum repository on RHEL"
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