Not reusing shadow models

[henrikfo]

Issue

Problem Description

When training shadow models and not using "training_data_fraction" = 0.5, e.g. 0.72, the shadow models is always retrained because they are trained with 0.5.

Expected Behavior

Should use "training_data_fraction" when selecting amount of data points to use when creating shadow models.

What Needs to be Done

Make construct_balanced_assignments() compatible with other splits than 50/50

How Can It Be Tested or Reproduced

Run examples/mia/cifar_main.ipynb and change training_data_fraction to something else than 0.5