private static <E> List<E> realizeFutures(Collection<Future<E>> futures)
      throws InterruptedException, ExecutionException {
    List<E> values = new ArrayList<>();
    for (Future<E> future : futures) {
      values.add(future.get());
    }
    return values;
  }
Starts building the steps to run.

@param buildContext the {@link BuildContext}
@return a new {@link StepsRunner}
jib-core/src/main/java/com/google/cloud/tools/jib/builder/steps/StepsRunner.java