Safer Refresh of Index Stats in CCR IT

We should only force merge after we know that an index is green and refresh after
forcemerge to ensure we get the latest stats in any case.

closes elastic#64167

x-pack/plugin/ccr/src/internalClusterTest/java/org/elasticsearch/xpack/ccr/CcrRepositoryIT.java

@@ -14,7 +14,6 @@
 import org.elasticsearch.action.admin.cluster.snapshots.restore.RestoreSnapshotRequest;
 import org.elasticsearch.action.admin.cluster.state.ClusterStateRequest;
 import org.elasticsearch.action.admin.cluster.state.ClusterStateResponse;
-import org.elasticsearch.action.admin.indices.forcemerge.ForceMergeResponse;
 import org.elasticsearch.action.admin.indices.stats.IndexStats;
 import org.elasticsearch.action.admin.indices.stats.IndicesStatsAction;
 import org.elasticsearch.action.admin.indices.stats.IndicesStatsRequest;
@@ -77,6 +76,7 @@
 import java.util.stream.Collectors;
 
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
+import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAllSuccessful;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertHitCount;
 import static org.hamcrest.Matchers.aMapWithSize;
 import static org.hamcrest.Matchers.equalTo;
@@ -489,13 +489,12 @@ public void testCcrRepositoryFetchesSnapshotShardSizeFromIndexShardStoreStats()
             assertThat(bulkRequest.get().hasFailures(), is(false));
         }
 
-        final ForceMergeResponse forceMergeResponse = leaderClient().admin().indices().prepareForceMerge(leaderIndex)
-            .setMaxNumSegments(1)
-            .setFlush(true)
-            .get();
-        assertThat(forceMergeResponse.getSuccessfulShards(), equalTo(numberOfShards));
-        assertThat(forceMergeResponse.getFailedShards(), equalTo(0));
         ensureLeaderGreen(leaderIndex);
+        assertAllSuccessful(leaderClient().admin().indices().prepareForceMerge(leaderIndex)
+                .setMaxNumSegments(1)
+                .setFlush(true)
+                .get());
+        refresh(leaderClient(), leaderIndex);
 
         final IndexStats indexStats = leaderClient().admin().indices().prepareStats(leaderIndex)
             .clear()