[SPARK-7498] [ML] removed varargs annotation from Params.setDefaults

In SPARK-7429 and PR https://github.com/apache/spark/pull/5960, I added the varargs annotation to Params.setDefault which takes a variable number of ParamPairs. It worked locally and on Jenkins for me.
However, mengxr reported issues compiling on his machine. So I'm reverting the change introduced in https://github.com/apache/spark/pull/5960 by removing varargs.

Author: Joseph K. Bradley <joseph@databricks.com>

Closes #6021 from jkbradley/revert-varargs and squashes the following commits:

098ed39 [Joseph K. Bradley] removed varargs annotation from Params.setDefaults taking multiple ParamPairs

mllib/src/main/scala/org/apache/spark/ml/param/params.scala

@@ -387,11 +387,12 @@ trait Params extends Identifiable with Serializable {
   /**
    * Sets default values for a list of params.
    *
+   * Note: Java developers should use the single-parameter [[setDefault()]].
+   *       Annotating this with varargs causes compilation failures. See SPARK-7498.
    * @param paramPairs  a list of param pairs that specify params and their default values to set
    *                    respectively. Make sure that the params are initialized before this method
    *                    gets called.
    */
-  @varargs
   protected final def setDefault(paramPairs: ParamPair[_]*): this.type = {
     paramPairs.foreach { p =>
       setDefault(p.param.asInstanceOf[Param[Any]], p.value)

mllib/src/test/java/org/apache/spark/ml/param/JavaTestParams.java

@@ -59,6 +59,5 @@ public class JavaTestParams extends JavaParams {
       ParamValidators.inArray(validStrings));
     setDefault(myIntParam, 1);
     setDefault(myDoubleParam, 0.5);
-    setDefault(myIntParam.w(1), myDoubleParam.w(0.5));
   }
 }