Automatic testing of tvla.py script

[abdullahvarici]

With the PR https://github.com/lowRISC/ot-sca/pull/95, we can now load histograms and use them for general test. This is done automatically when a PR is created but it does not cover all functionality of the tvla.py script. We should also add an automatic test which gets power measurements, computes their t-values and compares with the expected values.

In addition there may be some other functionalities of the tvla.py script that may be tested. Maybe @vrozic, @vogelpi and @andreaskurth has some ideas?