mock core scheduler interactions for shim unit tests

In the shim unit tests we start a full core scheduler. This leads to issues as when the full core is started we expect that there is a full working K8s cluster underneath.

This is not the case and should not be the case for the unit tests. We need to mock the core scheduler instead of starting the full scheduler. There should be no need for build in workaround by placing code in "if test skip this part".

The code should be robust enough to either handle the nil values that occur in tests or we need to return "empty" values.