add output to migrate-007, add script to revert it

@gwprice @e0d 

We need to re-run this in the test environment since it didn't exit cleanly, and we also need to see how it impacts normal traffic / performance (observed 5-10% locking while it was running).

These changes just add console output to the main migration, and a script we can use to revert the migration and re-run it.

One minor change to the migration, in addition, it will skip any threads whose `endorsed_response_count` has already been set.
 
I don't think we should limit this to things that don't have endorsed_reponse_count set, because it could be used to resolve data integrity issues after the first run