discourse_test: re-use bundled gems from the base file (#587)
discourse_test: re-use bundled gems from the base file (#587)

By doing `rm -rf .bundle` and `bundle install --standalone`, we were setting up bundle to install gems in `./bundle`. The base file installs gems in `./vendor/bundle`. That means that the test image was ending up with two complete copies of our dependencies.

This commit removes the `--standalone` command, and allows the `./vendor/bundle` artifacts to be re-used in the test image.
discourse/discourse_docker,discourse/discourse_docker,discourse/discourse_docker