[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.

1 files changed, 10 insertions, 15 deletions

diff --git a/external/kinesis-asl/src/main/scala/org/apache/spark/streaming/kinesis/KinesisRecordProcessor.scala b/external/kinesis-asl/src/main/scala/org/apache/spark/streaming/kinesis/KinesisRecordProcessor.scala
index 41c6ab123b..80e0cce055 100644
--- a/external/kinesis-asl/src/main/scala/org/apache/spark/streaming/kinesis/KinesisRecordProcessor.scala
+++ b/external/kinesis-asl/src/main/scala/org/apache/spark/streaming/kinesis/KinesisRecordProcessor.scala
@@ -73,7 +73,7 @@ private[kinesis] class KinesisRecordProcessor[T](receiver: KinesisReceiver[T], w
         logDebug(s"Stored: Worker $workerId stored ${batch.size} records for shardId $shardId")
         receiver.setCheckpointer(shardId, checkpointer)
       } catch {
-        case NonFatal(e) => {
+        case NonFatal(e) =>
           /*
            *  If there is a failure within the batch, the batch will not be checkpointed.
            *  This will potentially cause records since the last checkpoint to be processed
@@ -84,7 +84,6 @@ private[kinesis] class KinesisRecordProcessor[T](receiver: KinesisReceiver[T], w
 
           /* Rethrow the exception to the Kinesis Worker that is managing this RecordProcessor. */
           throw e
-        }
       }
     } else {
       /* RecordProcessor has been stopped. */
@@ -148,29 +147,25 @@ private[kinesis] object KinesisRecordProcessor extends Logging {
       /* If the function failed, either retry or throw the exception */
       case util.Failure(e) => e match {
         /* Retry:  Throttling or other Retryable exception has occurred */
-        case _: ThrottlingException | _: KinesisClientLibDependencyException if numRetriesLeft > 1
-          => {
-               val backOffMillis = Random.nextInt(maxBackOffMillis)
-               Thread.sleep(backOffMillis)
-               logError(s"Retryable Exception:  Random backOffMillis=${backOffMillis}", e)
-               retryRandom(expression, numRetriesLeft - 1, maxBackOffMillis)
-             }
+        case _: ThrottlingException | _: KinesisClientLibDependencyException
+            if numRetriesLeft > 1 =>
+          val backOffMillis = Random.nextInt(maxBackOffMillis)
+          Thread.sleep(backOffMillis)
+          logError(s"Retryable Exception:  Random backOffMillis=${backOffMillis}", e)
+          retryRandom(expression, numRetriesLeft - 1, maxBackOffMillis)
         /* Throw:  Shutdown has been requested by the Kinesis Client Library. */
-        case _: ShutdownException => {
+        case _: ShutdownException =>
           logError(s"ShutdownException:  Caught shutdown exception, skipping checkpoint.", e)
           throw e
-        }
         /* Throw:  Non-retryable exception has occurred with the Kinesis Client Library */
-        case _: InvalidStateException => {
+        case _: InvalidStateException =>
           logError(s"InvalidStateException:  Cannot save checkpoint to the DynamoDB table used" +
               s" by the Amazon Kinesis Client Library.  Table likely doesn't exist.", e)
           throw e
-        }
         /* Throw:  Unexpected exception has occurred */
-        case _ => {
+        case _ =>
           logError(s"Unexpected, non-retryable exception.", e)
           throw e
-        }
       }
     }
   }