[Zen2] fix NodeJoinTests#testConcurrentJoining() (#36033)

Today we sometimes create a setup in which the node is a quorum on its own,
which allows it to win a pre-voting round and schedule an election essentially
at will, causing it to discard all the joins it just received and fail the
test. This change excludes this case, preventing stray elections from ruining
things.

Author: DaveCTurner

server/src/test/java/org/elasticsearch/cluster/coordination/NodeJoinTests.java

@@ -70,6 +70,7 @@
 
 import static java.util.Collections.emptyList;
 import static java.util.Collections.emptyMap;
+import static java.util.Collections.singletonList;
 import static org.elasticsearch.transport.TransportService.HANDSHAKE_ACTION_NAME;
 import static org.hamcrest.Matchers.containsString;
 
@@ -418,12 +419,12 @@ public void testConcurrentJoining() {
         List<DiscoveryNode> nodes = IntStream.rangeClosed(1, randomIntBetween(2, 5))
             .mapToObj(nodeId -> newNode(nodeId, true)).collect(Collectors.toList());
 
-        VotingConfiguration votingConfiguration = new VotingConfiguration(
-            randomSubsetOf(randomIntBetween(1, nodes.size()), nodes).stream().map(DiscoveryNode::getId).collect(Collectors.toSet()));
+        DiscoveryNode localNode = nodes.get(0);
+        VotingConfiguration votingConfiguration = new VotingConfiguration(randomValueOtherThan(singletonList(localNode),
+            () -> randomSubsetOf(randomIntBetween(1, nodes.size()), nodes)).stream().map(DiscoveryNode::getId).collect(Collectors.toSet()));
 
         logger.info("Voting configuration: {}", votingConfiguration);
 
-        DiscoveryNode localNode = nodes.get(0);
         long initialTerm = randomLongBetween(1, 10);
         long initialVersion = randomLongBetween(1, 10);
         setupRealMasterServiceAndCoordinator(initialTerm, initialState(false, localNode, initialTerm, initialVersion, votingConfiguration));
@@ -488,12 +489,7 @@ public void testConcurrentJoining() {
                     } catch (InterruptedException | BrokenBarrierException e) {
                         throw new RuntimeException(e);
                     }
-                    try {
-                        joinNode(joinRequest);
-                    } catch (CoordinationStateRejectedException ignore) {
-                        // ignore: even the "correct" requests may fail as a duplicate because a concurrent election may cause a node to
-                        // spontaneously join.
-                    }
+                    joinNode(joinRequest);
                 }, "process " + joinRequest)).collect(Collectors.toList());
 
         assertionThread.start();