Fix exception when synchronizing remotely

We are lacking the proper prefixing of the command to issue with the remote command when synchronizing remotely, potentially resulting in an exception being raised because of a None being used. This change fixes the problem by using Repository.command to correctly prefix the commands issues by the _findSubvolPath function.

Author: d-e-s-o

btrfs-backup/src/deso/btrfs/repository.py

@@ -1,7 +1,7 @@
 # repository.py
 
 #/***************************************************************************
-# * Copyright (C) 2015-2017 Daniel Mueller (deso@posteo.net)  *
+# * Copyright (C) 2015-2017,2019 Daniel Mueller (deso@posteo.net) *
 # * *
 # * This program is free software: you can redistribute it and/or modify *
 # * it under the terms of the GNU General Public License as published by *
@@ -212,11 +212,14 @@ def _findSubvolPath(directory, repository):
  try:
  # We start off by looking up the ID of the subvolume containing the
  # given directory.
- output, _ = execute(*rootId(directory), stdout=b"", stderr=repository.stderr)
+ cmd = repository.command(rootId, directory)
+ output, _ = execute(*cmd, stdout=b"", stderr=repository.stderr)
  id_ = int(output[:-1])
+
  # One we have that ID we can look up the subvolume's path relative
  # to the btrfs root.
- output, _ = execute(*resolveId(id_, directory), stdout=b"", stderr=repository.stderr)
+ cmd = repository.command(resolveId, id_, directory)
+ output, _ = execute(*cmd, stdout=b"", stderr=repository.stderr)
  return output[:-1].decode("utf-8")
  except ProcessError:
  return None