[SPARK-9866][SQL] Speed up VersionsSuite by using persistent Ivy cache

This patch attempts to speed up VersionsSuite by storing fetched Hive JARs in an Ivy cache that persists across tests runs. If `SPARK_VERSIONS_SUITE_IVY_PATH` is set, that path will be used for the cache; if it is not set, VersionsSuite will create a temporary Ivy cache which is deleted after the test completes.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #9624 from JoshRosen/SPARK-9866.

sql/hive/src/test/scala/org/apache/spark/sql/hive/client/VersionsSuite.scala

@@ -36,10 +36,12 @@ import org.apache.spark.util.Utils
 @ExtendedHiveTest
 class VersionsSuite extends SparkFunSuite with Logging {
 
-  // Do not use a temp path here to speed up subsequent executions of the unit test during
-  // development.
-  private val ivyPath = Some(
-    new File(sys.props("java.io.tmpdir"), "hive-ivy-cache").getAbsolutePath())
+  // In order to speed up test execution during development or in Jenkins, you can specify the path
+  // of an existing Ivy cache:
+  private val ivyPath: Option[String] = {
+    sys.env.get("SPARK_VERSIONS_SUITE_IVY_PATH").orElse(
+      Some(new File(sys.props("java.io.tmpdir"), "hive-ivy-cache").getAbsolutePath))
+  }
 
   private def buildConf() = {
     lazy val warehousePath = Utils.createTempDir()