Fixing variables scope and leak parameter in documentation hyper notebook

[jodemaey]

Hi there,

While trying to reuse the code of the documentation for hyperparameters optimization, I found that the variables scopes for the datasets are not correct, with the objective function using variables defined in the global scope.

Also the notebook was crashing because in this function the leak rate is defined as lr but in the hyperopt_config dictionary it is defined as leak.

I thus propose some change so that this code works. I have checked that it runs correctly, but please double check that before any merging.

Cheers,

Jonathan