Update instructions for building QA image
This updates the instructions for building a QA Docker image, identical to https://gitlab.com/gitlab-org/gitlab/tree/master/qa#building-a-docker-image-to-test
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
This updates the instructions for building a QA Docker image, identical to https://gitlab.com/gitlab-org/gitlab/tree/master/qa#building-a-docker-image-to-test