[SPARK-17657][SQL] Disallow Users to Change Table Type

### What changes were proposed in this pull request?
Hive allows users to change the table type from `Managed` to `External` or from `External` to `Managed` by altering table's property `EXTERNAL`. See the JIRA: https://issues.apache.org/jira/browse/HIVE-1329

So far, Spark SQL does not correctly support it, although users can do it. Many assumptions are broken in the implementation. Thus, this PR is to disallow users to change it.

In addition, we also do not allow users to set the property `EXTERNAL` when creating a table.

### How was this patch tested?
Added test cases

Author: gatorsmile <gatorsmile@gmail.com>

Closes #15230 from gatorsmile/alterTableSetExternal.

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

@@ -112,6 +112,11 @@ private[spark] class HiveExternalCatalog(conf: SparkConf, hadoopConf: Configurat
         s"as table property keys may not start with '$DATASOURCE_PREFIX' or '$STATISTICS_PREFIX':" +
         s" ${invalidKeys.mkString("[", ", ", "]")}")
     }
+    // External users are not allowed to set/switch the table type. In Hive metastore, the table
+    // type can be switched by changing the value of a case-sensitive table property `EXTERNAL`.
+    if (table.properties.contains("EXTERNAL")) {
+      throw new AnalysisException("Cannot set or change the preserved property key: 'EXTERNAL'")
+    }
   }
 
   // --------------------------------------------------------------------------

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveDDLSuite.scala

@@ -315,6 +315,38 @@ class HiveDDLSuite
     assert(message.contains("Cannot alter a table with ALTER VIEW. Please use ALTER TABLE instead"))
   }
 
+  test("create table - SET TBLPROPERTIES EXTERNAL to TRUE") {
+    val tabName = "tab1"
+    withTable(tabName) {
+      val message = intercept[AnalysisException] {
+        sql(s"CREATE TABLE $tabName (height INT, length INT) TBLPROPERTIES('EXTERNAL'='TRUE')")
+      }.getMessage
+      assert(message.contains("Cannot set or change the preserved property key: 'EXTERNAL'"))
+    }
+  }
+
+  test("alter table - SET TBLPROPERTIES EXTERNAL to TRUE") {
+    val tabName = "tab1"
+    withTable(tabName) {
+      val catalog = spark.sessionState.catalog
+      sql(s"CREATE TABLE $tabName (height INT, length INT)")
+      assert(
+        catalog.getTableMetadata(TableIdentifier(tabName)).tableType == CatalogTableType.MANAGED)
+      val message = intercept[AnalysisException] {
+        sql(s"ALTER TABLE $tabName SET TBLPROPERTIES ('EXTERNAL' = 'TRUE')")
+      }.getMessage
+      assert(message.contains("Cannot set or change the preserved property key: 'EXTERNAL'"))
+      // The table type is not changed to external
+      assert(
+        catalog.getTableMetadata(TableIdentifier(tabName)).tableType == CatalogTableType.MANAGED)
+      // The table property is case sensitive. Thus, external is allowed
+      sql(s"ALTER TABLE $tabName SET TBLPROPERTIES ('external' = 'TRUE')")
+      // The table type is not changed to external
+      assert(
+        catalog.getTableMetadata(TableIdentifier(tabName)).tableType == CatalogTableType.MANAGED)
+    }
+  }
+
   test("alter views and alter table - misuse") {
     val tabName = "tab1"
     withTable(tabName) {