ISV Parallel U trainer

Created by: tiagofrepereira2012

In the ISV parallel toolchain ./bin/verify_isv the only step that is parallelized is the UBM training. There is no parallel implementation for the U matrix. For each EM iteration, this can be carried out as the following: E-step: for each parametric job, run the U [e_step] (https://www.idiap.ch/software/bob/docs/latest/bioidiap/bob.learn.em/master/py_api.html?highlight=isvtrainer#bob.learn.em.ISVTrainer.e_step) with a reduced set of the GMMStatistics and save the statistics:

• acc_u_a1
• [acc_u_a2] (https://www.idiap.ch/software/bob/docs/latest/bioidiap/bob.learn.em/master/py_api.html?highlight=isvtrainer#bob.learn.em.ISVTrainer.acc_u_a2)

M-Step: Sum all the saved statistics and run the m_step