Fix hyperopting bug that happens during multiprocessing

For some reason, the hyperopt process stops sometimes. The error is hard to trace, and I cannot make much sense of the error messages. To debug this, try the following configurations:

(disabled upload to cometml, epochs=4)

• basic launcher with n_jobs = 1 --> Works!
• joblib launcher with n_jobs = 1 --> fails (see comment below)
• basic launcher with n_jobs > 1
• joblib launcher with n_jobs > 1