Add kubernetes-server-mock test dependency

[andrewazores]

The unit tests for the KubernetesApiPlatformClient are lacking, mostly because it's currently quite a pain to set up all the mocks. There is a mock Kubernetes server that could help out a lot: https://itnext.io/mock-kubernetes-api-server-in-java-using-fabric8-kubernetes-mock-server-81a75cf6c47c

I think this might be best left for a follow-up PR.

Originally posted by @andrewazores in #492 (comment)

[andrewazores]

There is also an OpenShift equivalent:

https://github.com/fabric8io/kubernetes-client/tree/master/openshift-server-mock

This could be used for testing the OpenShiftAuthManager.