fix(s3): set default root path (close #2834)

drivers/s3/meta.go

@@ -21,6 +21,7 @@ type Addition struct {
 
 var config = driver.Config{
 	Name:        "S3",
+	DefaultRoot: "/",
 	LocalSort:   true,
 	CheckStatus: true,
 }

drivers/uss/meta.go

@@ -16,8 +16,9 @@ type Addition struct {
 }
 
 var config = driver.Config{
-	Name:      "USS",
-	LocalSort: true,
+	Name:        "USS",
+	LocalSort:   true,
+	DefaultRoot: "/",
 }
 
 func init() {