[pyclustering.cluster] Revise unit-tests for KMeans++ python implementation

[annoviko]

Introduction One of the tests is wrong, but pass (sample 4 should be instead of 3):

     def testInitializerForKmeansSampleSimple04(self):
        self.templateKmeansPlusPlusForClustering(SIMPLE_SAMPLES.SAMPLE_SIMPLE3, 5, [15, 15, 15, 15, 15])