Add parameter to shuffle test sets on each node during distributed training

[jfomhover]

When using libsvm2bin component, train and test files will be converted together in bin format. It results that for distributed, you have N training files and also N testing files, and both will have to be distributed one per node. But this use case occurs mainy when you use libsvm2bin, although it can be met in other scenarios as well.

This PR implements a parameter in the training module to shuffle the test files one per node, or to share all test files across all nodes. The idea is to use mode n_train_1_test when using common test files, but use n_train_n_test when the number of test files equals number of train files, and should be assigned to each node.