[ML] Resolve NetworkDisruptionIT (#43441)

After the network disruption a partition is created,
one side of which can form a cluster the other can't.
Ensure requests are sent to a node on the correct side
of the cluster

x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/integration/NetworkDisruptionIT.java

@@ -38,12 +38,6 @@ public class NetworkDisruptionIT extends BaseMlIntegTestCase {
         return plugins;
     }
 
-    // Remove this once the AwaitsFix below has been resolved
-    public void testDummy() {
-        assertTrue(true);
-    }
-
-    @AwaitsFix( bugUrl = "https://github.com/elastic/elasticsearch/issues/39858")
     public void testJobRelocation() throws Exception {
         internalCluster().ensureAtLeastNumDataNodes(5);
         ensureStableCluster(5);

x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/support/BaseMlIntegTestCase.java

@@ -353,7 +353,7 @@ public abstract class BaseMlIntegTestCase extends ESIntegTestCase {
     protected String awaitJobOpenedAndAssigned(String jobId, String queryNode) throws Exception {
 
         PersistentTasksClusterService persistentTasksClusterService =
-            internalCluster().getInstance(PersistentTasksClusterService.class, internalCluster().getMasterName());
+            internalCluster().getInstance(PersistentTasksClusterService.class, internalCluster().getMasterName(queryNode));
         // Speed up rechecks to a rate that is quicker than what settings would allow.
         // The check would work eventually without doing this, but the assertBusy() below
         // would need to wait 30 seconds, which would make the test run very slowly.