[SPARK-11783][SQL] Fixes execution Hive client when using remote Hive metastore

When using remote Hive metastore, `hive.metastore.uris` is set to the metastore URI.  However, it overrides `javax.jdo.option.ConnectionURL` unexpectedly, thus the execution Hive client connects to the actual remote Hive metastore instead of the Derby metastore created in the temporary directory.  Cleaning this configuration for the execution Hive client fixes this issue.

Author: Cheng Lian <lian@databricks.com>

Closes #9895 from liancheng/spark-11783.clean-remote-metastore-config.

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

@@ -736,6 +736,21 @@ private[hive] object HiveContext {
       s"jdbc:derby:;databaseName=${localMetastore.getAbsolutePath};create=true")
     propMap.put("datanucleus.rdbms.datastoreAdapterClassName",
       "org.datanucleus.store.rdbms.adapter.DerbyAdapter")
+
+    // SPARK-11783: When "hive.metastore.uris" is set, the metastore connection mode will be
+    // remote (https://cwiki.apache.org/confluence/display/Hive/AdminManual+MetastoreAdmin
+    // mentions that "If hive.metastore.uris is empty local mode is assumed, remote otherwise").
+    // Remote means that the metastore server is running in its own process.
+    // When the mode is remote, configurations like "javax.jdo.option.ConnectionURL" will not be
+    // used (because they are used by remote metastore server that talks to the database).
+    // Because execution Hive should always connects to a embedded derby metastore.
+    // We have to remove the value of hive.metastore.uris. So, the execution Hive client connects
+    // to the actual embedded derby metastore instead of the remote metastore.
+    // You can search HiveConf.ConfVars.METASTOREURIS in the code of HiveConf (in Hive's repo).
+    // Then, you will find that the local metastore mode is only set to true when
+    // hive.metastore.uris is not set.
+    propMap.put(ConfVars.METASTOREURIS.varname, "")
+
     propMap.toMap
   }