[SPARK-2328] [SQL] Add execution of `SHOW TABLES` before `TestHive.reset()`.

`PruningSuite` is executed first of Hive tests unfortunately, `TestHive.reset()` breaks the test environment.
To prevent this, we must run a query before calling reset the first time.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1268 from ueshin/issues/SPARK-2328 and squashes the following commits:

043ceac [Takuya UESHIN] Add execution of `SHOW TABLES` before `TestHive.reset()`.

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/PruningSuite.scala

@@ -26,6 +26,9 @@ import scala.collection.JavaConversions._
  * A set of test cases that validate partition and column pruning.
  */
 class PruningSuite extends HiveComparisonTest {
+  // MINOR HACK: You must run a query before calling reset the first time.
+  TestHive.hql("SHOW TABLES")
+
   // Column/partition pruning is not implemented for `InMemoryColumnarTableScan` yet, need to reset
   // the environment to ensure all referenced tables in this suites are not cached in-memory.
   // Refer to https://issues.apache.org/jira/browse/SPARK-2283 for details.