docker-api 1.8.2, fix remove_images, enable attach during build

- Updated to docker-api 1.8.2
- Fixed remove_images option, wasn't previously cleaning intermediate
  images
- Enabled attach build output during Docker::Image.build

Build process will show build progress at log level info - could update to only show at .debug if desired. Right now using JSON.parse to clean up the output but it ends up making some of the output goofy - alternative is to show the raw JSON stream which is more ugly IMO.