Fix ComponentTemplatesFileSettingsIT.testSettingsApplied (elastic#137669)

This is pretty much a copy of elastic#130869.

Since the cluster state API no longer runs on the master node, we need to wait for the cluster state publication to have finished before retrieving the cluster state.

Fixes elastic#137258

Author: nielsbauman

muted-tests.yml

@@ -423,9 +423,6 @@ tests:
 - class: org.elasticsearch.xpack.inference.DefaultEndPointsIT
   method: testMultipleInferencesTriggeringDownloadAndDeploy
   issue: https://github.com/elastic/elasticsearch/issues/117208
-- class: org.elasticsearch.reservedstate.service.ComponentTemplatesFileSettingsIT
-  method: testSettingsApplied
-  issue: https://github.com/elastic/elasticsearch/issues/137258
 - class: org.elasticsearch.xpack.esql.qa.mixed.EsqlClientYamlIT
   method: test {p0=esql/40_tsdb/error on rename timestamp}
   issue: https://github.com/elastic/elasticsearch/issues/137259

server/src/internalClusterTest/java/org/elasticsearch/reservedstate/service/ComponentTemplatesFileSettingsIT.java

@@ -386,6 +386,7 @@ private void assertClusterStateSaveOK(CountDownLatch savedClusterState, AtomicLo
         boolean awaitSuccessful = savedClusterState.await(20, TimeUnit.SECONDS);
         assertTrue(awaitSuccessful);
 
+        awaitMasterNode();
         final ClusterStateResponse clusterStateResponse = clusterAdmin().state(
             new ClusterStateRequest(TEST_REQUEST_TIMEOUT).waitForMetadataVersion(metadataVersion.get())
         ).actionGet();
@@ -532,8 +533,7 @@ public void testSettingsApplied() throws Exception {
         writeJSONFile(dataNode, testJSON);
 
         logger.info("--> start master node");
-        final String masterNode = internalCluster().startMasterOnlyNode();
-        awaitMasterNode(internalCluster().getNonMasterNodeName(), masterNode);
+        internalCluster().startMasterOnlyNode();
 
         assertClusterStateSaveOK(savedClusterState.v1(), savedClusterState.v2());