Wait for state publication in SLMFileSettingsIT.testSettingsApplied (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#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());