BUG: model creator hangs in MAD-X process

[Felix Soubelet]

As of last commit, the model_creator hangs in the MAD-X process as MAD-X itself does not find the input file.
The error message logged is

MADX | ++++++ Error: invalid input filename  :  lhc_model/job.create_model.madx | .madx_wrapper

As simple reproduction would be the example command from the OMC website (keep the -d flag):

python -d -m omc3.tbt_converter \
    --files trackone \
    --tbt_datatype trackone \
    --drop_elements LHCB1MSIA.EXIT.B1_P_ \
    --outputdir .