Fix hieradata for MySQL backup rotation
Fix hieradata for MySQL backup rotation

I believe this was misnamed when it was added and it should actually
be modifying the MySQL backup rotation we do in preview.

I think that automysqlbackup in preview will now keep less backups
than staging and production.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet