Look for Fs in the cache rather than calling NewFs directly

This will save operations when rclone is used in remote control mode
or with the same remote multiple times in the command line.

backend/union/union.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/ncw/rclone/fs"
+	"github.com/ncw/rclone/fs/cache"
 	"github.com/ncw/rclone/fs/config/configmap"
 	"github.com/ncw/rclone/fs/config/configstruct"
 	"github.com/ncw/rclone/fs/hash"
@@ -342,7 +343,7 @@ func NewFs(name, root string, m configmap.Mapper) (fs.Fs, error) {
 		if configName != "local" {
 			rootString = configName + ":" + rootString
 		}
-		myFs, err := fs.NewFs(rootString)
+		myFs, err := cache.Get(rootString)
 		if err != nil {
 			if err == fs.ErrorIsFile {
 				return myFs, err