SPARK-4430 [STREAMING] [TEST] Apache RAT Checks fail spuriously on test files

Another trivial one. The RAT failure was due to temp files from `FailureSuite` not being cleaned up. This just makes the cleanup more reliable by using the standard temp dir mechanism.

Author: Sean Owen <sowen@cloudera.com>

Closes #4189 from srowen/SPARK-4430 and squashes the following commits:

9ea63ff [Sean Owen] Properly acquire a temp directory to ensure it is cleaned up at shutdown, which helps avoid a RAT check failure

streaming/src/test/scala/org/apache/spark/streaming/FailureSuite.scala

@@ -28,21 +28,16 @@ import java.io.File
  */
 class FailureSuite extends TestSuiteBase with Logging {
 
-  var directory = "FailureSuite"
+  val directory = Utils.createTempDir().getAbsolutePath
   val numBatches = 30
 
   override def batchDuration = Milliseconds(1000)
 
   override def useManualClock = false
 
-  override def beforeFunction() {
-    super.beforeFunction()
-    Utils.deleteRecursively(new File(directory))
-  }
-
   override def afterFunction() {
-    super.afterFunction()
     Utils.deleteRecursively(new File(directory))
+    super.afterFunction()
   }
 
   test("multiple failures with map") {