Fix flaky test BulkIntegrationIT.testDeleteIndexWhileIndexing (#5491)

Signed-off-by: Poojita Raj <poojiraj@amazon.com>

Signed-off-by: Poojita Raj <poojiraj@amazon.com>
(cherry picked from commit 7108ee5)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

server/src/internalClusterTest/java/org/opensearch/action/bulk/BulkIntegrationIT.java

@@ -193,34 +193,29 @@ public void testDeleteIndexWhileIndexing() throws Exception {
         String index = "deleted_while_indexing";
         createIndex(index);
         AtomicBoolean stopped = new AtomicBoolean();
-        Thread[] threads = new Thread[between(1, 4)];
         AtomicInteger docID = new AtomicInteger();
-        for (int i = 0; i < threads.length; i++) {
-            threads[i] = new Thread(() -> {
-                while (stopped.get() == false && docID.get() < 5000) {
-                    String id = Integer.toString(docID.incrementAndGet());
-                    try {
-                        IndexResponse response = client().prepareIndex(index)
-                            .setId(id)
-                            .setSource(Collections.singletonMap("f" + randomIntBetween(1, 10), randomNonNegativeLong()), XContentType.JSON)
-                            .get();
-                        assertThat(response.getResult(), is(oneOf(CREATED, UPDATED)));
-                        logger.info("--> index id={} seq_no={}", response.getId(), response.getSeqNo());
-                    } catch (OpenSearchException ignore) {
-                        logger.info("--> fail to index id={}", id);
-                    }
+        Thread thread = new Thread(() -> {
+            while (stopped.get() == false && docID.get() < 5000) {
+                String id = Integer.toString(docID.incrementAndGet());
+                try {
+                    IndexResponse response = client().prepareIndex(index)
+                        .setId(id)
+                        .setSource(Collections.singletonMap("f" + randomIntBetween(1, 10), randomNonNegativeLong()), XContentType.JSON)
+                        .get();
+                    assertThat(response.getResult(), is(oneOf(CREATED, UPDATED)));
+                    logger.info("--> index id={} seq_no={}", response.getId(), response.getSeqNo());
+                } catch (OpenSearchException ignore) {
+                    logger.info("--> fail to index id={}", id);
                 }
-            });
-            threads[i].start();
-        }
+            }
+        });
+        thread.start();
         ensureGreen(index);
         assertBusy(() -> assertThat(docID.get(), greaterThanOrEqualTo(1)));
         assertAcked(client().admin().indices().prepareDelete(index));
         stopped.set(true);
-        for (Thread thread : threads) {
-            thread.join(ReplicationRequest.DEFAULT_TIMEOUT.millis() / 2);
-            assertFalse(thread.isAlive());
-        }
+        thread.join(ReplicationRequest.DEFAULT_TIMEOUT.millis() / 2);
+        assertFalse(thread.isAlive());
     }
 
 }