Add support for a list of k8s objects

[tqorange]

This PR adds support for yaml files with a list of k8s objects in them, for example:

apiVersion: v1
kind: List
items:
- apiVersion: v1
  kind: ConfigMap
  metadata:
    name: cf-one
- apiVersion: v1
  kind: ConfigMap
  metadata:
    name: cf-two

[tqorange]

Not sure if this was intentional, but this was only checking the first result. My fixture yaml initially failed this test.

[garethr]

Thanks, much appreciated. I'll get this into the next release.