refs #484 to configure CORS
Merge pull request #484 from S1E11/master

to enable CORS tag API
Allow Docker registry config to support yaml collections
Allow configurations to define listeners

A listener can receive the same notifications that the existing
search_backend receives by declaring a Listener() object that
may optionally implement the following methods:

    repository_created
    repository_updated
    repository_deleted
    tag_created
    tag_deleted

These are post-commit listeners and are not guaranteed delivery.
WIP Kubernetes integration
WIP Kubernetes/OpenShift integration part 2
Correct docker image reference