[SPARK-20282][SS][TESTS] Write the commit log first to fix a race contion in tests

## What changes were proposed in this pull request?

This PR fixes the following failure:
```
sbt.ForkMain$ForkError: org.scalatest.exceptions.TestFailedException:
Assert on query failed:

== Progress ==
   AssertOnQuery(<condition>, )
   StopStream
   AddData to MemoryStream[value#30891]: 1,2
   StartStream(OneTimeTrigger,org.apache.spark.util.SystemClock35cdc93a,Map())
   CheckAnswer: [6],[3]
   StopStream
=> AssertOnQuery(<condition>, )
   AssertOnQuery(<condition>, )
   StartStream(OneTimeTrigger,org.apache.spark.util.SystemClockcdb247d,Map())
   CheckAnswer: [6],[3]
   StopStream
   AddData to MemoryStream[value#30891]: 3
   StartStream(OneTimeTrigger,org.apache.spark.util.SystemClock55394e4d,Map())
   CheckLastBatch: [2]
   StopStream
   AddData to MemoryStream[value#30891]: 0
   StartStream(OneTimeTrigger,org.apache.spark.util.SystemClock749aa997,Map())
   ExpectFailure[org.apache.spark.SparkException, isFatalError: false]
   AssertOnQuery(<condition>, )
   AssertOnQuery(<condition>, incorrect start offset or end offset on exception)

== Stream ==
Output Mode: Append
Stream state: not started
Thread state: dead

== Sink ==
0: [6] [3]

== Plan ==

	at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:495)
	at org.scalatest.FunSuite.newAssertionFailedException(FunSuite.scala:1555)
	at org.scalatest.Assertions$class.fail(Assertions.scala:1328)
	at org.scalatest.FunSuite.fail(FunSuite.scala:1555)
	at org.apache.spark.sql.streaming.StreamTest$class.failTest$1(StreamTest.scala:347)
	at org.apache.spark.sql.streaming.StreamTest$class.verify$1(StreamTest.scala:318)
	at org.apache.spark.sql.streaming.StreamTest$$anonfun$liftedTree1$1$1.apply(StreamTest.scala:483)
	at org.apache.spark.sql.streaming.StreamTest$$anonfun$liftedTree1$1$1.apply(StreamTest.scala:357)
	at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
	at org.apache.spark.sql.streaming.StreamTest$class.liftedTree1$1(StreamTest.scala:357)
	at org.apache.spark.sql.streaming.StreamTest$class.testStream(StreamTest.scala:356)
	at org.apache.spark.sql.streaming.StreamingQuerySuite.testStream(StreamingQuerySuite.scala:41)
	at org.apache.spark.sql.streaming.StreamingQuerySuite$$anonfun$6.apply$mcV$sp(StreamingQuerySuite.scala:166)
	at org.apache.spark.sql.streaming.StreamingQuerySuite$$anonfun$6.apply(StreamingQuerySuite.scala:161)
	at org.apache.spark.sql.streaming.StreamingQuerySuite$$anonfun$6.apply(StreamingQuerySuite.scala:161)
	at org.apache.spark.sql.catalyst.util.package$.quietly(package.scala:42)
	at org.apache.spark.sql.test.SQLTestUtils$$anonfun$testQuietly$1.apply$mcV$sp(SQLTestUtils.scala:268)
	at org.apache.spark.sql.test.SQLTestUtils$$anonfun$testQuietly$1.apply(SQLTestUtils.scala:268)
	at org.apache.spark.sql.test.SQLTestUtils$$anonfun$testQuietly$1.apply(SQLTestUtils.scala:268)
	at org.scalatest.Transformer$$anonfun$apply$1.apply$mcV$sp(Transformer.scala:22)
	at org.scalatest.OutcomeOf$class.outcomeOf(OutcomeOf.scala:85)
	at org.scalatest.OutcomeOf$.outcomeOf(OutcomeOf.scala:104)
	at org.scalatest.Transformer.apply(Transformer.scala:22)
	at org.scalatest.Transformer.apply(Transformer.scala:20)
	at org.scalatest.FunSuiteLike$$anon$1.apply(FunSuiteLike.scala:166)
	at org.apache.spark.SparkFunSuite.withFixture(SparkFunSuite.scala:68)
	at org.scalatest.FunSuiteLike$class.invokeWithFixture$1(FunSuiteLike.scala:163)
	at org.scalatest.FunSuiteLike$$anonfun$runTest$1.apply(FunSuiteLike.scala:175)
	at org.scalatest.FunSuiteLike$$anonfun$runTest$1.apply(FunSuiteLike.scala:175)
	at org.scalatest.SuperEngine.runTestImpl(Engine.scala:306)
	at org.scalatest.FunSuiteLike$class.runTest(FunSuiteLike.scala:175)
	at org.apache.spark.sql.streaming.StreamingQuerySuite.org$scalatest$BeforeAndAfterEach$$super$runTest(StreamingQuerySuite.scala:41)
	at org.scalatest.BeforeAndAfterEach$class.runTest(BeforeAndAfterEach.scala:255)
	at org.apache.spark.sql.streaming.StreamingQuerySuite.org$scalatest$BeforeAndAfter$$super$runTest(StreamingQuerySuite.scala:41)
	at org.scalatest.BeforeAndAfter$class.runTest(BeforeAndAfter.scala:200)
	at org.apache.spark.sql.streaming.StreamingQuerySuite.runTest(StreamingQuerySuite.scala:41)
	at org.scalatest.FunSuiteLike$$anonfun$runTests$1.apply(FunSuiteLike.scala:208)
	at org.scalatest.FunSuiteLike$$anonfun$runTests$1.apply(FunSuiteLike.scala:208)
	at org.scalatest.SuperEngine$$anonfun$traverseSubNodes$1$1.apply(Engine.scala:413)
	at org.scalatest.SuperEngine$$anonfun$traverseSubNodes$1$1.apply(Engine.scala:401)
	at scala.collection.immutable.List.foreach(List.scala:381)
	at org.scalatest.SuperEngine.traverseSubNodes$1(Engine.scala:401)
	at org.scalatest.SuperEngine.org$scalatest$SuperEngine$$runTestsInBranch(Engine.scala:396)
	at org.scalatest.SuperEngine.runTestsImpl(Engine.scala:483)
	at org.scalatest.FunSuiteLike$class.runTests(FunSuiteLike.scala:208)
	at org.scalatest.FunSuite.runTests(FunSuite.scala:1555)
	at org.scalatest.Suite$class.run(Suite.scala:1424)
	at org.scalatest.FunSuite.org$scalatest$FunSuiteLike$$super$run(FunSuite.scala:1555)
	at org.scalatest.FunSuiteLike$$anonfun$run$1.apply(FunSuiteLike.scala:212)
	at org.scalatest.FunSuiteLike$$anonfun$run$1.apply(FunSuiteLike.scala:212)
	at org.scalatest.SuperEngine.runImpl(Engine.scala:545)
	at org.scalatest.FunSuiteLike$class.run(FunSuiteLike.scala:212)
	at org.apache.spark.SparkFunSuite.org$scalatest$BeforeAndAfterAll$$super$run(SparkFunSuite.scala:31)
	at org.scalatest.BeforeAndAfterAll$class.liftedTree1$1(BeforeAndAfterAll.scala:257)
	at org.scalatest.BeforeAndAfterAll$class.run(BeforeAndAfterAll.scala:256)
	at org.apache.spark.sql.streaming.StreamingQuerySuite.org$scalatest$BeforeAndAfter$$super$run(StreamingQuerySuite.scala:41)
	at org.scalatest.BeforeAndAfter$class.run(BeforeAndAfter.scala:241)
	at org.apache.spark.sql.streaming.StreamingQuerySuite.run(StreamingQuerySuite.scala:41)
	at org.scalatest.tools.Framework.org$scalatest$tools$Framework$$runSuite(Framework.scala:357)
	at org.scalatest.tools.Framework$ScalaTestTask.execute(Framework.scala:502)
	at sbt.ForkMain$Run$2.call(ForkMain.java:296)
	at sbt.ForkMain$Run$2.call(ForkMain.java:286)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
```

The failure is because `CheckAnswer` will run once `committedOffsets` is updated. Then writing the commit log may be interrupted by the following `StopStream`.

This PR just change the order to write the commit log first.

## How was this patch tested?

Jenkins

Author: Shixiong Zhu <[email protected]>

Closes #17594 from zsxwing/SPARK-20282.

Author: zsxwing

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamExecution.scala

@@ -304,8 +304,8 @@ class StreamExecution(
               finishTrigger(dataAvailable)
               if (dataAvailable) {
                 // Update committed offsets.
-                committedOffsets ++= availableOffsets
                 batchCommitLog.add(currentBatchId)
+                committedOffsets ++= availableOffsets
                 logDebug(s"batch ${currentBatchId} committed")
                 // We'll increase currentBatchId after we complete processing current batch's data
                 currentBatchId += 1