This fixes the bug in the _get_role_name method; Travis's environment is at "/home/travis/build/edx/configuration/...", so identifying the Docker image/play name by grabbing the next token after the first instance of the word "build" is incorrect, as it resolves to "edx", instead of the name of the Docker image. Instead, we look for the first token after "docker/build". This also address the duplicate output bug, where, if docker_plays and modified_docker_files have images in common, they would be printed twice.