[SPARK-12273][STREAMING] Make Spark Streaming web UI list Receivers in order

Currently the Streaming web UI does NOT list Receivers in order; however, it seems more convenient for the users if Receivers are listed in order.

![spark-12273](https://cloud.githubusercontent.com/assets/15843379/11736602/0bb7f7a8-a00b-11e5-8e86-96ba9297fb12.png)

Author: proflin <proflin.me@gmail.com>

Closes #10264 from proflin/Spark-12273.

streaming/src/main/scala/org/apache/spark/streaming/ui/StreamingPage.scala

@@ -392,8 +392,9 @@ private[ui] class StreamingPage(parent: StreamingTab)
       maxX: Long,
       minY: Double,
       maxY: Double): Seq[Node] = {
-    val content = listener.receivedEventRateWithBatchTime.map { case (streamId, eventRates) =>
-      generateInputDStreamRow(jsCollector, streamId, eventRates, minX, maxX, minY, maxY)
+    val content = listener.receivedEventRateWithBatchTime.toList.sortBy(_._1).map {
+      case (streamId, eventRates) =>
+        generateInputDStreamRow(jsCollector, streamId, eventRates, minX, maxX, minY, maxY)
     }.foldLeft[Seq[Node]](Nil)(_ ++ _)
 
     // scalastyle:off