[py] Allow changing of the temporary directory

RuntimeError: File - constructor: C++ exception caught: 'cannot open file `/tmp/tmpep2b12y5/biometric_references/103.hdf5''

@ydayer I believe this change might be responsible for breaking at least the LGBPHS pipeline. Either with of without specifying a -T temp_directory, it crashes with an error message of the type ``` RuntimeError: File - constructor: C++ exception caught: 'cannot open file `/tmp/tmpep2b12y5/biometric_references/103.hdf5'' ```

Thanks for reporting this @lcolbois I'll have a look into that this afternoon. Cheers