RemoveClusterServiceTests fails on unexpected exception

[nik9000]

https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+master+periodic/4334/consoleFull

Throwable #1: java.lang.IllegalStateException: No node available for cluster: cluster_2
 	at __randomizedtesting.SeedInfo.seed([5164832263D0A921:B4E416B95DD80128]:0)
 	at org.elasticsearch.transport.RemoteClusterConnection$ConnectedNodes.get(RemoteClusterConnection.java:674)
 	at org.elasticsearch.transport.RemoteClusterConnection.lambda$collectNodes$1(RemoteClusterConnection.java:208)
 	at org.elasticsearch.transport.RemoteClusterConnection.collectNodes(RemoteClusterConnection.java:241)
 	at org.elasticsearch.transport.RemoteClusterService.collectNodes(RemoteClusterService.java:359)
 	at org.elasticsearch.transport.RemoteClusterServiceTests.testCollectNodes(RemoteClusterServiceTests.java:394)
 	at java.lang.Thread.run(Thread.java:748)

Looks like there is a race condition between shutting down the connection and the test. This path makes it look like the connection is still in place but doesn't have any nodes connected. I'm not sure if the code should be changed to call the listener or the test should be changed to catch the exception.