@VisibleForTesting
  Path getBuildFile() {
    if (buildFileUnprocessed == null) {
      return contextRoot.resolve("jib.yaml");
    }
    return buildFileUnprocessed;
  }
Returns a user configured Path to a buildfile and if none is configured returns jib.yaml in
{@link #contextRoot}.

@return a path to a buildfile
jib-cli/src/main/java/com/google/cloud/tools/jib/cli/Build.java