allow to mount virtual folders on root (/) path

Fixes #783

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

vfs/osfs.go

@@ -46,7 +46,7 @@ func NewOsFs(connectionID, rootDir, mountPath string) Fs {
 		name:         osFsName,
 		connectionID: connectionID,
 		rootDir:      rootDir,
-		mountPath:    mountPath,
+		mountPath:    getMountPath(mountPath),
 	}
 }