Add ability to load Vagrant project.yaml

For Vagrant-based deploys, we want to remove the need to have the
config repo present.

If env.provider_zone contains 'vagrant', load a local project.yaml
file from ./vagrant/project.yaml
No need for regex, simplify
use vagrant/cotton.yaml for clarity
Merge pull request #43 from ministryofjustice/vagrant_project_yaml

Add ability to load Vagrant project.yaml