vfs: convert vfs options to new style

This also
- move in use options (Opt) from vfsflags to vfscommon
- change os.FileMode to vfscommon.FileMode in parameters
- rework vfscommon.FileMode and add tests

cmd/serve/docker/driver.go

@@ -19,7 +19,6 @@ import (
 	"github.com/rclone/rclone/lib/atexit"
 	"github.com/rclone/rclone/lib/file"
 	"github.com/rclone/rclone/vfs/vfscommon"
-	"github.com/rclone/rclone/vfs/vfsflags"
 )
 
 // Driver implements docker driver api
@@ -55,7 +54,7 @@ func NewDriver(ctx context.Context, root string, mntOpt *mountlib.Options, vfsOp
 		mntOpt = &mountlib.Opt
 	}
 	if vfsOpt == nil {
-		vfsOpt = &vfsflags.Opt
+		vfsOpt = &vfscommon.Opt
 	}
 	drv := &Driver{
 		root:      root,