Wait for state publication in SLMFileSettingsIT.testSettingsApplied (#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 #130853

Author: nielsbauman

muted-tests.yml

@@ -502,9 +502,6 @@ tests:
 - class: org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT
   method: test {p0=mtermvectors/10_basic/Tests catching other exceptions per item}
   issue: https://github.com/elastic/elasticsearch/issues/122414
-- class: org.elasticsearch.xpack.slm.SLMFileSettingsIT
-  method: testSettingsApplied
-  issue: https://github.com/elastic/elasticsearch/issues/130853
 - class: org.elasticsearch.cluster.ClusterStateSerializationTests
   method: testSerializationPreMultiProject
   issue: https://github.com/elastic/elasticsearch/issues/130872

x-pack/plugin/slm/src/internalClusterTest/java/org/elasticsearch/xpack/slm/SLMFileSettingsIT.java

@@ -186,6 +186,7 @@ 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())
         ).get();
@@ -229,8 +230,7 @@ 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());