Major Description
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 do it.
