Eliminate warnings from deprecated BisectingKMeansModel.computeCost

[warn] /Users/maxim/proj/kmeans-computeCost-warning/mllib/src/test/scala/org/apache/spark/ml/clustering/BisectingKMeansSuite.scala:108: method computeCost in class BisectingKMeansModel is deprecated (since 3.0.0): This method is deprecated and will be removed in future versions. Use ClusteringEvaluator instead. You can also get the cost on the training dataset in the summary.
[warn]     assert(model.computeCost(dataset) < 0.1)
[warn]                  ^
[warn] /Users/maxim/proj/kmeans-computeCost-warning/mllib/src/test/scala/org/apache/spark/ml/clustering/BisectingKMeansSuite.scala:135: method computeCost in class BisectingKMeansModel is deprecated (since 3.0.0): This method is deprecated and will be removed in future versions. Use ClusteringEvaluator instead. You can also get the cost on the training dataset in the summary.
[warn]     assert(model.computeCost(dataset) == summary.trainingCost)
[warn]                  ^
[warn] /Users/maxim/proj/kmeans-computeCost-warning/mllib/src/test/scala/org/apache/spark/ml/clustering/BisectingKMeansSuite.scala:323: method computeCost in class BisectingKMeansModel is deprecated (since 3.0.0): This method is deprecated and will be removed in future versions. Use ClusteringEvaluator instead. You can also get the cost on the training dataset in the summary.
[warn]       model.computeCost(dataset)
[warn]             ^
[warn] three warnings found