[SPARK-20260][MLLIB] String interpolation required for error message

## What changes were proposed in this pull request?
This error message doesn't get properly formatted because of a missing `s`.  Currently the error looks like:

```
Caused by: java.lang.IllegalArgumentException: requirement failed: indices should be one-based and in ascending order; found current=$current, previous=$previous; line="$line"
```
(note the literal `$current` instead of the interpolated value)

Please review http://spark.apache.org/contributing.html

 before opening a pull request.

Author: Vijay Ramesh <vramesh@demandbase.com>

Closes #17572 from vijaykramesh/master.

(cherry picked from commit 261eaf51)
Signed-off-by: Sean Owen <sowen@cloudera.com>

core/src/main/scala/org/apache/spark/deploy/SparkHadoopUtil.scala

@@ -373,7 +373,7 @@ class SparkHadoopUtil extends Logging {
       }
     } catch {
       case e: IOException =>
-        logDebug("Failed to decode $token: $e", e)
+        logDebug(s"Failed to decode $token: $e", e)
     }
     buffer.toString
   }

mllib-local/src/test/scala/org/apache/spark/ml/util/TestingUtils.scala

@@ -207,7 +207,7 @@ object TestingUtils {
       if (r.fun(x, r.y, r.eps)) {
         throw new TestFailedException(
           s"Did not expect \n$x\n and \n${r.y}\n to be within " +
-            "${r.eps}${r.method} for all elements.", 0)
+            s"${r.eps}${r.method} for all elements.", 0)
       }
       true
     }

mllib/src/main/scala/org/apache/spark/mllib/clustering/PowerIterationClustering.scala

@@ -259,7 +259,7 @@ object PowerIterationClustering extends Logging {
         val j = ctx.dstId
         val s = ctx.attr
         if (s < 0.0) {
-          throw new SparkException("Similarity must be nonnegative but found s($i, $j) = $s.")
+          throw new SparkException(s"Similarity must be nonnegative but found s($i, $j) = $s.")
         }
         if (s > 0.0) {
           ctx.sendToSrc(s)
@@ -283,7 +283,7 @@ object PowerIterationClustering extends Logging {
     : Graph[Double, Double] = {
     val edges = similarities.flatMap { case (i, j, s) =>
       if (s < 0.0) {
-        throw new SparkException("Similarity must be nonnegative but found s($i, $j) = $s.")
+        throw new SparkException(s"Similarity must be nonnegative but found s($i, $j) = $s.")
       }
       if (i != j) {
         Seq(Edge(i, j, s), Edge(j, i, s))

mllib/src/main/scala/org/apache/spark/mllib/tree/model/DecisionTreeModel.scala

@@ -248,7 +248,7 @@ object DecisionTreeModel extends Loader[DecisionTreeModel] with Logging {
       // Build node data into a tree.
       val trees = constructTrees(nodes)
       assert(trees.length == 1,
-        "Decision tree should contain exactly one tree but got ${trees.size} trees.")
+        s"Decision tree should contain exactly one tree but got ${trees.size} trees.")
       val model = new DecisionTreeModel(trees(0), Algo.fromString(algo))
       assert(model.numNodes == numNodes, s"Unable to load DecisionTreeModel data from: $dataPath." +
         s" Expected $numNodes nodes but found ${model.numNodes}")

mllib/src/main/scala/org/apache/spark/mllib/util/MLUtils.scala

@@ -119,7 +119,7 @@ object MLUtils extends Logging {
     while (i < indicesLength) {
       val current = indices(i)
       require(current > previous, s"indices should be one-based and in ascending order;"
-        + " found current=$current, previous=$previous; line=\"$line\"")
+        + s""" found current=$current, previous=$previous; line="$line"""")
       previous = current
       i += 1
     }

mllib/src/test/scala/org/apache/spark/mllib/util/TestingUtils.scala

@@ -207,7 +207,7 @@ object TestingUtils {
       if (r.fun(x, r.y, r.eps)) {
         throw new TestFailedException(
           s"Did not expect \n$x\n and \n${r.y}\n to be within " +
-            "${r.eps}${r.method} for all elements.", 0)
+            s"${r.eps}${r.method} for all elements.", 0)
       }
       true
     }

sql/hive/src/test/scala/org/apache/spark/sql/hive/orc/OrcQuerySuite.scala

@@ -283,7 +283,7 @@ class OrcQuerySuite extends QueryTest with BeforeAndAfterAll with OrcTest {
       val queryOutput = selfJoin.queryExecution.analyzed.output
 
       assertResult(4, "Field count mismatches")(queryOutput.size)
-      assertResult(2, "Duplicated expression ID in query plan:\n $selfJoin") {
+      assertResult(2, s"Duplicated expression ID in query plan:\n $selfJoin") {
         queryOutput.filter(_.name == "_1").map(_.exprId).size
       }
 
@@ -292,7 +292,7 @@ class OrcQuerySuite extends QueryTest with BeforeAndAfterAll with OrcTest {
   }
 
   test("nested data - struct with array field") {
-    val data = (1 to 10).map(i => Tuple1((i, Seq("val_$i"))))
+    val data = (1 to 10).map(i => Tuple1((i, Seq(s"val_$i"))))
     withOrcTable(data, "t") {
       checkAnswer(sql("SELECT `_1`.`_2`[0] FROM t"), data.map {
         case Tuple1((_, Seq(string))) => Row(string)
@@ -301,7 +301,7 @@ class OrcQuerySuite extends QueryTest with BeforeAndAfterAll with OrcTest {
   }
 
   test("nested data - array of struct") {
-    val data = (1 to 10).map(i => Tuple1(Seq(i -> "val_$i")))
+    val data = (1 to 10).map(i => Tuple1(Seq(i -> s"val_$i")))
     withOrcTable(data, "t") {
       checkAnswer(sql("SELECT `_1`[0].`_2` FROM t"), data.map {
         case Tuple1(Seq((_, string))) => Row(string)