[SPARK-7684] [SQL] Refactoring MetastoreDataSourcesSuite to workaround SPARK-7684

As stated in SPARK-7684, currently `TestHive.reset` has some execution order specific bug, which makes running specific test suites locally pretty frustrating. This PR refactors `MetastoreDataSourcesSuite` (which relies on `TestHive.reset` heavily) using various `withXxx` utility methods in `SQLTestUtils` to ask each test case to cleanup their own mess so that we can avoid calling `TestHive.reset`.

Author: Cheng Lian <lian@databricks.com>
Author: Yin Huai <yhuai@databricks.com>

Closes #6353 from liancheng/workaround-spark-7684 and squashes the following commits:

26939aa [Yin Huai] Move the initialization of jsonFilePath to beforeAll.
a423d48 [Cheng Lian] Fixes Scala style issue
dfe45d0 [Cheng Lian] Refactors MetastoreDataSourcesSuite to workaround SPARK-7684
92a116d [Cheng Lian] Fixes minor styling issues

sql/core/src/test/scala/org/apache/spark/sql/QueryTest.scala

@@ -67,6 +67,10 @@ class QueryTest extends PlanTest {
     checkAnswer(df, Seq(expectedAnswer))
   }
 
+  protected def checkAnswer(df: DataFrame, expectedAnswer: DataFrame): Unit = {
+    checkAnswer(df, expectedAnswer.collect())
+  }
+
   def sqlTest(sqlString: String, expectedAnswer: Seq[Row])(implicit sqlContext: SQLContext) {
     test(sqlString) {
       checkAnswer(sqlContext.sql(sqlString), expectedAnswer)

sql/core/src/test/scala/org/apache/spark/sql/test/SQLTestUtils.scala

@@ -75,14 +75,18 @@ trait SQLTestUtils {
   /**
    * Drops temporary table `tableName` after calling `f`.
    */
-  protected def withTempTable(tableName: String)(f: => Unit): Unit = {
-    try f finally sqlContext.dropTempTable(tableName)
+  protected def withTempTable(tableNames: String*)(f: => Unit): Unit = {
+    try f finally tableNames.foreach(sqlContext.dropTempTable)
   }
 
   /**
    * Drops table `tableName` after calling `f`.
    */
-  protected def withTable(tableName: String)(f: => Unit): Unit = {
-    try f finally sqlContext.sql(s"DROP TABLE IF EXISTS $tableName")
+  protected def withTable(tableNames: String*)(f: => Unit): Unit = {
+    try f finally {
+      tableNames.foreach { name =>
+        sqlContext.sql(s"DROP TABLE IF EXISTS $name")
+      }
+    }
   }
 }