Update GradientDescentSuite.scala

use more faster way to construct an array

Author: baishuo(白硕) <vc_java@hotmail.com>

Closes apache#588 from baishuo/master and squashes the following commits:

45b95fb [baishuo(白硕)] Update GradientDescentSuite.scala
c03b61c [baishuo(白硕)] Update GradientDescentSuite.scala
b666d27 [baishuo(白硕)] Update GradientDescentSuite.scala
(cherry picked from commit 0c19bb1)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>

mllib/src/test/scala/org/apache/spark/mllib/optimization/GradientDescentSuite.scala

@@ -81,11 +81,11 @@ class GradientDescentSuite extends FunSuite with LocalSparkContext with ShouldMa
     // Add a extra variable consisting of all 1.0's for the intercept.
     val testData = GradientDescentSuite.generateGDInput(A, B, nPoints, 42)
     val data = testData.map { case LabeledPoint(label, features) =>
-      label -> Vectors.dense(1.0, features.toArray: _*)
+      label -> Vectors.dense(1.0 +: features.toArray)
     }
 
     val dataRDD = sc.parallelize(data, 2).cache()
-    val initialWeightsWithIntercept = Vectors.dense(1.0, initialWeights: _*)
+    val initialWeightsWithIntercept = Vectors.dense(1.0 +: initialWeights.toArray)
 
     val (_, loss) = GradientDescent.runMiniBatchSGD(
       dataRDD,
@@ -111,7 +111,7 @@ class GradientDescentSuite extends FunSuite with LocalSparkContext with ShouldMa
     // Add a extra variable consisting of all 1.0's for the intercept.
     val testData = GradientDescentSuite.generateGDInput(2.0, -1.5, 10000, 42)
     val data = testData.map { case LabeledPoint(label, features) =>
-      label -> Vectors.dense(1.0, features.toArray: _*)
+      label -> Vectors.dense(1.0 +: features.toArray)
     }
 
     val dataRDD = sc.parallelize(data, 2).cache()