fs/multipart: save metadata(fs.json) for multipart uploads. (#2450)

fs-v1-multipart.go

@@ -255,7 +255,6 @@ func (fs fsObjects) newMultipartUpload(bucket string, object string, meta map[st
 //
 // Implements S3 compatible initiate multipart API.
 func (fs fsObjects) NewMultipartUpload(bucket, object string, meta map[string]string) (string, error) {
-	meta = make(map[string]string) // Reset the meta value, we are not going to save headers for fs.
 	// Verify if bucket name is valid.
 	if !IsValidBucketName(bucket) {
 		return "", BucketNameInvalid{Bucket: bucket}