[SPARK-14783] Preserve full exception stacktrace in IsolatedClientLoader

In IsolatedClientLoader, we have a`catch` block which throws an exception without wrapping the original exception, causing the full exception stacktrace and any nested exceptions to be lost. This patch fixes this, improving the usefulness of classloading error messages.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #12548 from JoshRosen/improve-logging-for-hive-classloader-issues.

sql/hive/src/main/scala/org/apache/spark/sql/hive/client/IsolatedClientLoader.scala

@@ -263,7 +263,7 @@ private[hive] class IsolatedClientLoader(
           throw new ClassNotFoundException(
             s"$cnf when creating Hive client using classpath: ${execJars.mkString(", ")}\n" +
             "Please make sure that jars for your version of hive and hadoop are included in the " +
-            s"paths passed to ${HiveContext.HIVE_METASTORE_JARS}.")
+            s"paths passed to ${HiveContext.HIVE_METASTORE_JARS}.", e)
         } else {
           throw e
         }