[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.

2 files changed, 5 insertions, 12 deletions

diff --git a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
index 86c6405522..e953a6e8ef 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
@@ -1153,14 +1153,12 @@ class DataFrameSuite extends QueryTest with SharedSQLContext {
   private def verifyNonExchangingAgg(df: DataFrame) = {
     var atFirstAgg: Boolean = false
     df.queryExecution.executedPlan.foreach {
-      case agg: TungstenAggregate => {
+      case agg: TungstenAggregate =>
         atFirstAgg = !atFirstAgg
-      }
-      case _ => {
+      case _ =>
         if (atFirstAgg) {
           fail("Should not have operators between the two aggregations")
         }
-      }
     }
   }
 
@@ -1170,12 +1168,11 @@ class DataFrameSuite extends QueryTest with SharedSQLContext {
   private def verifyExchangingAgg(df: DataFrame) = {
     var atFirstAgg: Boolean = false
     df.queryExecution.executedPlan.foreach {
-      case agg: TungstenAggregate => {
+      case agg: TungstenAggregate =>
         if (atFirstAgg) {
           fail("Should not have back to back Aggregates")
         }
         atFirstAgg = true
-      }
       case e: ShuffleExchange => atFirstAgg = false
       case _ =>
     }
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/execution/vectorized/ColumnarBatchSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/execution/vectorized/ColumnarBatchSuite.scala
index 8a551cd78c..31b63f2ce1 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/execution/vectorized/ColumnarBatchSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/execution/vectorized/ColumnarBatchSuite.scala
@@ -612,23 +612,20 @@ class ColumnarBatchSuite extends SparkFunSuite {
             val a2 = r2.getList(v._2).toArray
             assert(a1.length == a2.length, "Seed = " + seed)
             childType match {
-              case DoubleType => {
+              case DoubleType =>
                 var i = 0
                 while (i < a1.length) {
                   assert(doubleEquals(a1(i).asInstanceOf[Double], a2(i).asInstanceOf[Double]),
                     "Seed = " + seed)
                   i += 1
                 }
-              }
-              case FloatType => {
+              case FloatType =>
                 var i = 0
                 while (i < a1.length) {
                   assert(doubleEquals(a1(i).asInstanceOf[Float], a2(i).asInstanceOf[Float]),
                     "Seed = " + seed)
                   i += 1
                 }
-              }
-
               case t: DecimalType =>
                 var i = 0
                 while (i < a1.length) {
@@ -640,7 +637,6 @@ class ColumnarBatchSuite extends SparkFunSuite {
                   }
                   i += 1
                 }
-
               case _ => assert(a1 === a2, "Seed = " + seed)
             }
           case StructType(childFields) =>