[SPARK-15705][SQL] Change the default value of spark.sql.hive.convertMetastoreOrc to false.

## What changes were proposed in this pull request?
In 2.0, we add a new logic to convert HiveTableScan on ORC tables to Spark's native code path. However, during this conversion, we drop the original metastore schema (https://issues.apache.org/jira/browse/SPARK-15705). Because of this regression, I am changing the default value of `spark.sql.hive.convertMetastoreOrc` to false.

Author: Yin Huai <yhuai@databricks.com>

Closes #14267 from yhuai/SPARK-15705-changeDefaultValue.

sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveUtils.scala

@@ -97,10 +97,11 @@ private[spark] object HiveUtils extends Logging {
       .createWithDefault(false)
 
   val CONVERT_METASTORE_ORC = SQLConfigBuilder("spark.sql.hive.convertMetastoreOrc")
+    .internal()
     .doc("When set to false, Spark SQL will use the Hive SerDe for ORC tables instead of " +
       "the built in support.")
     .booleanConf
-    .createWithDefault(true)
+    .createWithDefault(false)
 
   val HIVE_METASTORE_SHARED_PREFIXES = SQLConfigBuilder("spark.sql.hive.metastore.sharedPrefixes")
     .doc("A comma separated list of class prefixes that should be loaded using the classloader " +