Use absolute rather than relative path for config.yml
Use absolute rather than relative path for config.yml

The relative path is relative to the files/ directory and so the include
breaks if that directory is deleted.

https://groups.google.com/forum/#!topic/ansible-project/MzSZLYhx5AY

Therefore seems more robust to switch to an absolute path making use of
`playbook_dir`.

toby-griffiths/mac-dev-playbook,annikaC/mac-dev-playbook