fix httpclient leaking

Signed-off-by: Lantao Jin <ltjin@amazon.com>

Author: LantaoJin

integ-test/src/test/java/org/opensearch/sql/legacy/OpenSearchSQLRestTestCase.java

@@ -311,7 +311,9 @@ protected static void configureHttpsClient(
    * cluster.
    */
   public void configureMultiClusters(String remote) throws IOException {
-    initRemoteClient(remote);
+    if (remoteClient == null) {
+      initRemoteClient(remote);
+    }
 
     Request connectionRequest = new Request("PUT", "_cluster/settings");
     String connectionSetting =