Integration test

[glyn]

As pointed out in https://github.com/pivotal/kubernetes-image-mapper/pull/2/files#r348191945, controller runtime has a standard way of implementing integration tests. We should consider adding an integration test, particularly if there are scenarios which turn out to be hard to unit test.

[glyn]

With kube-apiserver v1.15.5 and earlier, I get an intermittent error in the integration tests:

ERROR	controller-runtime.metrics	failed to register metric	{"name": "workqueue_retries_total", "queue": "imagemap", "error": "duplicate metrics collector registration attempted"}

(full logs). This may be related to kubernetes/kubernetes#76956, so I'm asking on kubernetes slack where to get v1.16.x of kube-apiserver to see if that helps.

[glyn]

Also seeing an intermittent/frequent integration test failure where an image map cannot be created because it is still being deleted. This happens even if I wait after the deletion until I can no longer get the image map. More investigation needed...