Use --restrict-to-repository instead of --restrict-to-path

[Ravinou]

No description provided.

[matthijskooijman]

Looks good, but I'm surprised about the mkdir. Did you test that this was required? Because the borg-serve manpage says:

       --restrict-to-repository PATH
              restrict repository access. Only the repository located at PATH (no sub-directories are considered) is accessible. Can be specified multiple times to allow the client access to  several
              repositories.  Unlike --restrict-to-path sub-directories are not accessible; PATH needs to directly point at a repository location. PATH may be an empty directory or the last element of
              PATH may not exist, in which case the client may initialize a repository there.

Which suggests the path does not need to exist.