[SPARK-2590][SQL] Added option to handle incremental collection, disabled by default

JIRA issue: [SPARK-2590](https://issues.apache.org/jira/browse/SPARK-2590)

Author: Cheng Lian <[email protected]>

Closes #1853 from liancheng/inc-collect-option and squashes the following commits:

cb3ea45 [Cheng Lian] Moved incremental collection option to Thrift server
43ce3aa [Cheng Lian] Changed incremental collect option name
623abde [Cheng Lian] Added option to handle incremental collection, disabled by default

(cherry picked from commit 21a95ef)
Signed-off-by: Michael Armbrust <[email protected]>

Author: liancheng

sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/server/SparkSQLOperationManager.scala

@@ -132,7 +132,16 @@ class SparkSQLOperationManager(hiveContext: HiveContext) extends OperationManage
           logDebug(result.queryExecution.toString())
           val groupId = round(random * 1000000).toString
           hiveContext.sparkContext.setJobGroup(groupId, statement)
-          iter = result.queryExecution.toRdd.toLocalIterator
+          iter = {
+            val resultRdd = result.queryExecution.toRdd
+            val useIncrementalCollect =
+              hiveContext.getConf("spark.sql.thriftServer.incrementalCollect", "false").toBoolean
+            if (useIncrementalCollect) {
+              resultRdd.toLocalIterator
+            } else {
+              resultRdd.collect().iterator
+            }
+          }
           dataTypes = result.queryExecution.analyzed.output.map(_.dataType).toArray
           setHasResultSet(true)
         } catch {