KubeVirt backend is not authenticated

FakeFish handles incoming credentials by passing them down
to scripts. This works for real hardware because in the end it's up to
the BMC to validate them. However, KubeVirt relies on a KUBECONFIG file
mounted to the container and completely ignores the credentials. This allows any user of the cluster to control VMs of the
user that created fakefish, power them on and off, and mount arbitrary CD
images to them.