[SPARK-2917] [SQL] Avoid table creation in logical plan analyzing for CTAS

This actually isn't the semantic we want.  All DDL commands should act as _actions_ and be executed immediately.  It is only when there is an EXPLAIN that we should not run the command eagerly.

I think `InsertIntoCreatedTable` should inherit from `Command` so that this happens automatically.  I'd also consider renaming it `InsertIntoCreatedTable` as you did with the physical operator.