[SPARK-5460][MLlib] Wrapped `Try` around `deleteAllCheckpoints` - RandomForest.

Because `deleteAllCheckpoints` has IOException potential.
fix issue.

Author: x1- <viva008@gmail.com>

Closes #4347 from x1-/SPARK-5460 and squashes the following commits:

7a3d8de [x1-] change `Try()` to `try catch { case ... }` ar RandomForest.
3a52745 [x1-] modified typo. 'faild' -> 'failed' and remove disused '-'.
1572576 [x1-] Wrapped `Try` around `deleteAllCheckpoints` - RandomForest.

mllib/src/main/scala/org/apache/spark/mllib/tree/RandomForest.scala

@@ -17,6 +17,8 @@
 
 package org.apache.spark.mllib.tree
 
+import java.io.IOException
+
 import scala.collection.mutable
 import scala.collection.JavaConverters._
 
@@ -244,7 +246,12 @@ private class RandomForest (
 
     // Delete any remaining checkpoints used for node Id cache.
     if (nodeIdCache.nonEmpty) {
-      nodeIdCache.get.deleteAllCheckpoints()
+      try {
+        nodeIdCache.get.deleteAllCheckpoints()
+      } catch {
+        case e:IOException =>
+          logWarning(s"delete all chackpoints failed. Error reason: ${e.getMessage}")
+      }
     }
 
     val trees = topNodes.map(topNode => new DecisionTreeModel(topNode, strategy.algo))