Support Conversion from ACID to EXTERNAL table

[dstreev]

Convert ACID table to EXTERNAL table.

Steps:

• RENAME ACID table (<original_name>_to_delete)
• CETAS from ACID table to 'name' that matches the original ACID table name.

Location of EXTERNAL table will go to default location base on Metastore configurations or the Database "LOCATION".

Cleanup of ACID table will be up to user.

[dstreev]

Translation to EXTERNAL table 'without' a STORED AS ... clause will default to 'textfiles'. So we need to pick up the serde on the source acid table and ensure the same for the external table.

[dstreev]

There are two facets to this:

1. Convert 'inplace' ACID tables.
2. Convert 'migrated' tables.

For the migrated option where the table is ACID on the LEFT, it should be converted to EXTERNAL/PURGE on the RIGHT. I see this second scenario being accomplished by adding a 'option' to -ma|-mao call 'TO_EXTERNAL'.