fix using accesspoint in ManagedUpload (#3109)

Author: AllanZhengYP

.changes/next-release/bugfix-Access Point-5e44acab.json

@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "Access Point",
+  "description": "Avoid mixing up S3 client config set by ManagedUpload with user-set client config"
+}

lib/s3/managed_upload.js

@@ -284,7 +284,7 @@ AWS.S3.ManagedUpload = AWS.util.inherit({
       self.service = new AWS.S3({params: params});
     } else {
       var service = self.service;
-      var config = AWS.util.copy(service.config);
+      var config = AWS.util.copy(service._originalConfig || {});
       config.signatureVersion = service.getSignatureVersion();
       self.service = new service.constructor.__super__(config);
       self.service.config.params =