[SPARK-13601] [TESTS] use 1 partition in tests to avoid race conditions

## What changes were proposed in this pull request?

Fix race conditions when cleanup files.

## How was this patch tested?

Existing tests.

Author: Davies Liu <davies@databricks.com>

Closes #11507 from davies/flaky.

Author: Davies Liu

sql/hive/src/test/scala/org/apache/spark/sql/sources/CommitFailureTestRelationSuite.scala

@@ -51,7 +51,7 @@ class CommitFailureTestRelationSuite extends SQLTestUtils with TestHiveSingleton
     withTempPath { file =>
       // fail the job in the middle of writing
       val divideByZero = udf((x: Int) => { x / (x - 1)})
-      val df = sqlContext.range(0, 10).select(divideByZero(col("id")))
+      val df = sqlContext.range(0, 10).coalesce(1).select(divideByZero(col("id")))
 
       SimpleTextRelation.callbackCalled = false
       intercept[SparkException] {
@@ -69,7 +69,8 @@ class CommitFailureTestRelationSuite extends SQLTestUtils with TestHiveSingleton
     withTempPath { file =>
       // fail the job in the middle of writing
       val divideByZero = udf((x: Int) => { x / (x - 1)})
-      val df = sqlContext.range(0, 10).select(col("id").mod(2).as("key"), divideByZero(col("id")))
+      val df = sqlContext.range(0, 10).coalesce(1)
+        .select(col("id").mod(2).as("key"), divideByZero(col("id")))
 
       SimpleTextRelation.callbackCalled = false
       intercept[SparkException] {
@@ -87,7 +88,7 @@ class CommitFailureTestRelationSuite extends SQLTestUtils with TestHiveSingleton
     SimpleTextRelation.failCommitter = false
     withTempPath { file =>
       // fail the job in the middle of writing
-      val df = sqlContext.range(0, 10).select(col("id").mod(2).as("key"), col("id"))
+      val df = sqlContext.range(0, 10).coalesce(1).select(col("id").mod(2).as("key"), col("id"))
 
       SimpleTextRelation.callbackCalled = false
       SimpleTextRelation.failWriter = true