Fix tests depending on _ilm/status API

Since elastic#129367 we run the `_ilm/status` API on the local node, which
could cause issues in tests that assume the API runs on the master node
- i.e. they assumed that once the assertion passed, all nodes in the
cluster would have that cluster state, which is not true.

Author: nielsbauman

test/framework/src/main/java/org/elasticsearch/test/rest/ESRestTestCase.java

@@ -1056,7 +1056,7 @@ private void wipeCluster() throws Exception {
         deleteAllNodeShutdownMetadata();
     }
 
-    private void waitForClusterUpdates() throws Exception {
+    public void waitForClusterUpdates() throws Exception {
         logger.info("Waiting for all cluster updates up to this moment to be processed");
 
         try {

x-pack/plugin/ilm/qa/multi-node/src/javaRestTest/java/org/elasticsearch/xpack/MigrateToDataTiersIT.java

@@ -169,6 +169,8 @@ public void testMigrateToDataTiersAction() throws Exception {
             Response response = client().performRequest(new Request("GET", "_ilm/status"));
             assertThat(EntityUtils.toString(response.getEntity()), containsString(OperationMode.STOPPED.toString()));
         });
+        // Wait for cluster state to be published to all nodes.
+        waitForClusterUpdates();
 
         String indexWithDataWarmRouting = "indexwithdatawarmrouting";
         Settings.Builder settings = Settings.builder()
@@ -340,6 +342,8 @@ public void testIndexTemplatesMigration() throws Exception {
                 Response response = client().performRequest(new Request("GET", "_ilm/status"));
                 assertThat(EntityUtils.toString(response.getEntity()), containsString(OperationMode.STOPPED.toString()));
             });
+            // Wait for cluster state to be published to all nodes.
+            waitForClusterUpdates();
         }
 
         Request migrateRequest = new Request("POST", "_ilm/migrate_to_data_tiers");

x-pack/plugin/ilm/qa/multi-node/src/javaRestTest/java/org/elasticsearch/xpack/ilm/TimeSeriesLifecycleActionsIT.java

@@ -766,6 +766,8 @@ public void testCanStopILMWithPolicyUsingNonexistentPolicy() throws Exception {
             String status = (String) statusResponseMap.get("operation_mode");
             assertEquals("STOPPED", status);
         });
+        // Wait for cluster state to be published to all nodes.
+        waitForClusterUpdates();
 
         // Re-start ILM so that subsequent tests don't fail
         Request startILMRequest = new Request("POST", "_ilm/start");