Log more data for PrevalidateShardPathIT#testCheckShards (elastic#109887

)

`PrevalidateShardPathIT#testCheckShards` still keeps failing on CI, so we need more logging.

* Add debug logging for `MasterService` events to verify that a cluster service update is triggered.
* Log explanation for stuck shards regardless whether they are located on node_2 in the cluster state.

See elastic#104807

muted-tests.yml

@@ -67,9 +67,6 @@ tests:
 - class: "org.elasticsearch.xpack.shutdown.NodeShutdownReadinessIT"
   issue: "https://github.com/elastic/elasticsearch/issues/109838"
   method: "testShutdownReadinessService"
-- class: "org.elasticsearch.cluster.PrevalidateShardPathIT"
-  issue: "https://github.com/elastic/elasticsearch/issues/104807"
-  method: "testCheckShards"
 - class: "org.elasticsearch.packaging.test.RpmPreservationTests"
   issue: "https://github.com/elastic/elasticsearch/issues/109898"
   method: "test30PreserveConfig"
@@ -82,6 +79,7 @@ tests:
   issue: "https://github.com/elastic/elasticsearch/issues/109915"
   method: "testRandomMultiValuesTopN"
 
+
 # Examples:
 #
 #  Mute a single test case in a YAML test suite:

server/src/internalClusterTest/java/org/elasticsearch/cluster/PrevalidateShardPathIT.java

@@ -22,6 +22,7 @@
 import org.elasticsearch.common.xcontent.ChunkedToXContent;
 import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.test.ESIntegTestCase;
+import org.elasticsearch.test.junit.annotations.TestLogging;
 
 import java.util.HashSet;
 import java.util.List;
@@ -39,6 +40,10 @@
 @ESIntegTestCase.ClusterScope(scope = ESIntegTestCase.Scope.TEST, numDataNodes = 0)
 public class PrevalidateShardPathIT extends ESIntegTestCase {
 
+    @TestLogging(
+        value = "org.elasticsearch.cluster.service.MasterService:DEBUG",
+        reason = "https://github.com/elastic/elasticsearch/issues/104807"
+    )
     public void testCheckShards() throws Exception {
         internalCluster().startMasterOnlyNode();
         String node1 = internalCluster().startDataOnlyNode();
@@ -95,7 +100,6 @@ public void testCheckShards() throws Exception {
                         .allShards()
                         .filter(s -> s.getIndexName().equals(indexName))
                         .filter(s -> node2ShardIds.contains(s.shardId()))
-                        .filter(s -> s.currentNodeId().equals(node2Id))
                         .toList();
                     logger.info("Found {} shards on the relocation source node {} in the cluster state", node2Shards, node2Id);
                     for (var node2Shard : node2Shards) {