improvement: parallelize get bucket and get object

lib/storage/metadata/mongoclient/MongoClientInterface.js

@@ -250,32 +250,47 @@ class MongoClientInterface {
     }
 
     getBucketAndObject(bucketName, objName, params, log, cb) {
+        return async.parallel({
+            bucket: callback => {
                 this.getBucketAttributes(bucketName, log, (err, bucket) => {
                     if (err) {
                         log.error(
-                    'getBucketAttributes: error getting bucket attributes',
+                            'getBucketAndObject: error getting bucket attrs',
                             { error: err.message });
-                return cb(err);
+                        return callback(err);
                     }
+                    return callback(null, bucket);
+                });
+            },
+            obj: callback => {
                 this.getObject(bucketName, objName, params, log, (err, obj) => {
                     if (err) {
                         if (err === errors.NoSuchKey) {
+                            return callback(null, null);
+                        }
+                        log.error('getBucketAndObject: error getting object',
+                                  { error: err.message });
+                        return callback(err);
+                    }
+                    return callback(null, obj);
+                });
+            },
+        }, (err, results) => {
+            if (err) {
+                return cb(errors.InternalError);
+            }
+            const { bucket, obj } = results;
+            if (!obj) {
                 return cb(null,
                           { bucket:
                             BucketInfo.fromObj(bucket).serialize(),
                           });
             }
-                    log.error('getObject: error getting object',
-                    { error: err.message });
-                    return cb(err);
-                }
             return cb(null, {
                 bucket: BucketInfo.fromObj(bucket).serialize(),
                 obj: JSON.stringify(obj),
             });
         });
-            return undefined;
-        });
     }
 
     putBucketAttributes(bucketName, bucketMD, log, cb) {