Fix reschedule async fsync test

This commit fixes the reschedule async fsync test in index service
tests. This test was passing for the wrong reason. Namely, the test was
trying to set translog durability to async, fire off an indexing
request, and then assert that the translog eventually got fsynced. The
problem here is that in the course of issuing the indexing request, a
mapping update is trigger. The mapping update triggers the index
settings to be refreshed. Since the test did not issue a cluster state
update to change the durability from request to async but instead did
this directly through index service, the mapping update flops the
durability back to async. This means that when the indexing request
executes, an fsync is performed after the request and the assertoin that
an fsync is not needed passes but for the wrong reason (in short: the
test wanted it to pass because an async fsync fired, but instead it
passed because a request async fired). This commit fixes this by going
through the index settings API so that a proper cluster state update is
triggered and so the mapping update does not flop the durability back to
request.

core/src/test/java/org/elasticsearch/index/IndexServiceTests.java

@@ -238,31 +238,43 @@ public void testAsyncFsyncActuallyWorks() throws Exception {
     }
 
     public void testRescheduleAsyncFsync() throws Exception {
-        Settings settings = Settings.builder()
-            .put(IndexSettings.INDEX_TRANSLOG_SYNC_INTERVAL_SETTING.getKey(), "100ms") // very often :)
-            .put(IndexSettings.INDEX_TRANSLOG_DURABILITY_SETTING.getKey(), Translog.Durability.REQUEST)
+        final Settings settings = Settings.builder()
+                .put(IndexSettings.INDEX_TRANSLOG_SYNC_INTERVAL_SETTING.getKey(), "100ms")
+                .put(IndexSettings.INDEX_TRANSLOG_DURABILITY_SETTING.getKey(), Translog.Durability.REQUEST)
             .build();
-        IndexService indexService = createIndex("test", settings);
+        final IndexService indexService = createIndex("test", settings);
         ensureGreen("test");
         assertNull(indexService.getFsyncTask());
-        IndexMetaData metaData = IndexMetaData.builder(indexService.getMetaData()).settings(Settings.builder().put(indexService.getMetaData().getSettings()).put(IndexSettings.INDEX_TRANSLOG_DURABILITY_SETTING.getKey(), Translog.Durability.ASYNC)).build();
-        indexService.updateMetaData(metaData);
+
+        client()
+                .admin()
+                .indices()
+                .prepareUpdateSettings("test")
+                .setSettings(Settings.builder().put(IndexSettings.INDEX_TRANSLOG_DURABILITY_SETTING.getKey(), Translog.Durability.ASYNC))
+                .get();
+
         assertNotNull(indexService.getFsyncTask());
-        assertTrue(indexService.getRefreshTask().mustReschedule());
+        assertTrue(indexService.getFsyncTask().mustReschedule());
         client().prepareIndex("test", "test", "1").setSource("{\"foo\": \"bar\"}", XContentType.JSON).get();
-        IndexShard shard = indexService.getShard(0);
-        assertBusy(() -> {
-            assertFalse(shard.getTranslog().syncNeeded());
-        });
-
-        metaData = IndexMetaData.builder(indexService.getMetaData()).settings(Settings.builder().put(indexService.getMetaData().getSettings()).put(IndexSettings.INDEX_TRANSLOG_DURABILITY_SETTING.getKey(), Translog.Durability.REQUEST)).build();
-        indexService.updateMetaData(metaData);
+        assertNotNull(indexService.getFsyncTask());
+        final IndexShard shard = indexService.getShard(0);
+        assertBusy(() -> assertFalse(shard.getTranslog().syncNeeded()));
+
+        client()
+                .admin()
+                .indices()
+                .prepareUpdateSettings("test")
+                .setSettings(Settings.builder().put(IndexSettings.INDEX_TRANSLOG_DURABILITY_SETTING.getKey(), Translog.Durability.REQUEST))
+                .get();
         assertNull(indexService.getFsyncTask());
 
-        metaData = IndexMetaData.builder(indexService.getMetaData()).settings(Settings.builder().put(indexService.getMetaData().getSettings()).put(IndexSettings.INDEX_TRANSLOG_DURABILITY_SETTING.getKey(), Translog.Durability.ASYNC)).build();
-        indexService.updateMetaData(metaData);
+        client()
+                .admin()
+                .indices()
+                .prepareUpdateSettings("test")
+                .setSettings(Settings.builder().put(IndexSettings.INDEX_TRANSLOG_DURABILITY_SETTING.getKey(), Translog.Durability.ASYNC))
+                .get();
         assertNotNull(indexService.getFsyncTask());
-
     }
 
     public void testIllegalFsyncInterval() {