Remove the assumption that a node's name == its hostname

[jan-g]

As per https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/#built-in-node-labels

[[[ Note: The value of these labels is cloud provider specific and is not guaranteed to be reliable. For example, the value of kubernetes.io/hostname may be the same as the node name in some environments and a different value in other environments. ]]]

(This is a quick handwave in the direction of #413)