[SPARK-25893][SQL] Show a directional error message for unsupported Hive Metastore versions

## What changes were proposed in this pull request?

When `spark.sql.hive.metastore.version` is misconfigured, we had better give a directional error message.

**BEFORE**
```scala
scala> sql("show databases").show
scala.MatchError: 2.4 (of class java.lang.String)
```

**AFTER**
```scala
scala> sql("show databases").show
java.lang.UnsupportedOperationException: Unsupported Hive Metastore version (2.4).
Please set spark.sql.hive.metastore.version with a valid version.
```

## How was this patch tested?

Manual.

Closes apache#22902 from dongjoon-hyun/SPARK-25893.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

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

@@ -100,6 +100,9 @@ private[hive] object IsolatedClientLoader extends Logging {
     case "2.1" | "2.1.0" | "2.1.1" => hive.v2_1
     case "2.2" | "2.2.0" => hive.v2_2
     case "2.3" | "2.3.0" | "2.3.1" | "2.3.2" | "2.3.3" => hive.v2_3
+    case version =>
+      throw new UnsupportedOperationException(s"Unsupported Hive Metastore version ($version). " +
+        s"Please set ${HiveUtils.HIVE_METASTORE_VERSION.key} with a valid version.")
   }
 
   private def downloadVersion(