Rake Task db:structure:load does not create schema for test db.

- The redifined structure:load task was using the wrong config, should
be using current_config, otherwise it reloads the structure for development if you just run `rake db:test:prepare`
- Tests (test_postgres, test_sqlite3) successful.
- This was tested against master
- Running Rails 3.2.14
- JRuby 1.7.4
- No backtraces, but the test schema would be empty before this fix