[SPARK-14508][BUILD] Add a new ScalaStyle Rule `OmitBracesInCase`

## What changes were proposed in this pull request?

According to the [Spark Code Style Guide](https://cwiki.apache.org/confluence/display/SPARK/Spark+Code+Style+Guide) and [Scala Style Guide](http://docs.scala-lang.org/style/control-structures.html#curlybraces), we had better enforce the following rule.
  ```
  case: Always omit braces in case clauses.
  ```
This PR makes a new ScalaStyle rule, 'OmitBracesInCase', and enforces it to the code.

## How was this patch tested?

Pass the Jenkins tests (including Scala style checking)

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #12280 from dongjoon-hyun/SPARK-14508.

3 files changed, 4 insertions, 8 deletions

diff --git a/streaming/src/test/scala/org/apache/spark/streaming/BasicOperationsSuite.scala b/streaming/src/test/scala/org/apache/spark/streaming/BasicOperationsSuite.scala
index bd60059b18..cfcbdc7c38 100644
--- a/streaming/src/test/scala/org/apache/spark/streaming/BasicOperationsSuite.scala
+++ b/streaming/src/test/scala/org/apache/spark/streaming/BasicOperationsSuite.scala
@@ -538,10 +538,9 @@ class BasicOperationsSuite extends TestSuiteBase {
         val stateObj = state.getOrElse(new StateObject)
         values.sum match {
           case 0 => stateObj.expireCounter += 1 // no new values
-          case n => { // has new values, increment and reset expireCounter
+          case n => // has new values, increment and reset expireCounter
             stateObj.counter += n
             stateObj.expireCounter = 0
-          }
         }
         stateObj.expireCounter match {
           case 2 => None // seen twice with no new values, give it the boot
diff --git a/streaming/src/test/scala/org/apache/spark/streaming/CheckpointSuite.scala b/streaming/src/test/scala/org/apache/spark/streaming/CheckpointSuite.scala
index fbb25d4c59..bdbac64b9b 100644
--- a/streaming/src/test/scala/org/apache/spark/streaming/CheckpointSuite.scala
+++ b/streaming/src/test/scala/org/apache/spark/streaming/CheckpointSuite.scala
@@ -267,10 +267,9 @@ class CheckpointSuite extends TestSuiteBase with DStreamCheckpointTester
     assert(!stateStream.checkpointData.currentCheckpointFiles.isEmpty,
       "No checkpointed RDDs in state stream before first failure")
     stateStream.checkpointData.currentCheckpointFiles.foreach {
-      case (time, file) => {
+      case (time, file) =>
         assert(fs.exists(new Path(file)), "Checkpoint file '" + file +"' for time " + time +
             " for state stream before first failure does not exist")
-      }
     }
 
     // Run till a further time such that previous checkpoint files in the stream would be deleted
@@ -297,10 +296,9 @@ class CheckpointSuite extends TestSuiteBase with DStreamCheckpointTester
     assert(!stateStream.checkpointData.currentCheckpointFiles.isEmpty,
       "No checkpointed RDDs in state stream before second failure")
     stateStream.checkpointData.currentCheckpointFiles.foreach {
-      case (time, file) => {
+      case (time, file) =>
         assert(fs.exists(new Path(file)), "Checkpoint file '" + file +"' for time " + time +
           " for state stream before seconds failure does not exist")
-      }
     }
     ssc.stop()
 
diff --git a/streaming/src/test/scala/org/apache/spark/streaming/MasterFailureTest.scala b/streaming/src/test/scala/org/apache/spark/streaming/MasterFailureTest.scala
index 29bee4adf2..60c8e70235 100644
--- a/streaming/src/test/scala/org/apache/spark/streaming/MasterFailureTest.scala
+++ b/streaming/src/test/scala/org/apache/spark/streaming/MasterFailureTest.scala
@@ -382,11 +382,10 @@ class FileGeneratingThread(input: Seq[String], testDir: Path, interval: Long)
                 fs.rename(tempHadoopFile, hadoopFile)
             done = true
           } catch {
-            case ioe: IOException => {
+            case ioe: IOException =>
                   fs = testDir.getFileSystem(new Configuration())
                   logWarning("Attempt " + tries + " at generating file " + hadoopFile + " failed.",
                     ioe)
-            }
           }
         }
         if (!done) {