Added more unit like test that verifies that has_child is never cached even if wrapped by another filter.
Throw exception if `cluster.name` is specified in TestCluster node settings

We rely on the `cluster.name` setting to be the same across all nodes
and transport clients etc. If a node setting contains `cluster.name`
the test might not work if a random transport client is swapped
in. Passing such a configuration should result in an exception since
it's clearly an illegal state.