added back compatable constructor to NaiveBayesModel to fix MIMA test failure

Author: leahmcguire

mllib/src/main/scala/org/apache/spark/mllib/classification/NaiveBayes.scala

@@ -62,6 +62,9 @@ class NaiveBayesModel private[mllib] (
     val theta: Array[Array[Double]],
     val modelType: NaiveBayesModels) extends ClassificationModel with Serializable with Saveable {
 
+  def this(labels: Array[Double], pi: Array[Double], theta: Array[Array[Double]]) =
+    this(labels, pi, theta, NaiveBayesModels.Multinomial)
+
   private val brzPi = new BDV[Double](pi)
   private val brzTheta = new BDM(theta(0).length, theta.length, theta.flatten).t