[google|dns] Add Project resource

- Add Project models, requests and tests
[google|dns] Add Zone model

- Add Zone model and test
- Refactor zone mock request to use a single Hash
- create_managed_zone requires description, don't default it to blank
- Fix indentation
[google|dns] Add Record resource

- Add Record models, requests and tests
- Add #record method (and associated test) to Zone
[google|dns] Add Change resource

- Add Change models, requests and tests
- Add #changes method (and associated test) to Zone
- Add #destroy method (and associated test) to Zone
- Add #modify method (and associated test) to Zone
- Add #save method (and associated test) to Zone
[google|dns] Add examples
Merge pull request #3195 from frodenas/gce_dns

[google|dns] Add missing models, requests and tests