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

vfs/vfs.go

@@ -204,7 +204,7 @@ func New(f fs.Fs, opt *vfscommon.Options) *VFS {
 	if opt != nil {
 		vfs.Opt = *opt
 	} else {
-		vfs.Opt = vfscommon.DefaultOpt
+		vfs.Opt = vfscommon.Opt
 	}
 
 	// Fill out anything else
@@ -776,7 +776,7 @@ func (vfs *VFS) AddVirtual(remote string, size int64, isDir bool) (err error) {
 	} else {
 		// Create parent of virtual directory since backend can't have empty directories
 		parent, leaf = path.Split(remote)
-		dir, err = vfs.mkdirAll(parent, vfs.Opt.DirPerms)
+		dir, err = vfs.mkdirAll(parent, os.FileMode(vfs.Opt.DirPerms))
 	}
 	if err != nil {
 		return err