Loosen the check for mounted volumes

Docker apparently does not always use the same mounted volume type

Fixes #352

storage/local.py

@@ -157,7 +157,6 @@ class LocalStorage(BaseStorageV2):
     # Verify that the storage's root path is under a mounted Docker volume.
     for mount in mounts:
       if mount.mountpoint != '/' and self._root_path.startswith(mount.mountpoint):
-        if mount.device == 'tmpfs':
         return
 
     raise Exception('Storage path %s is not under a mounted volume.\n\n'