[devicelab] Refactor devicelab using repo_util. Bug: https://github.com/flutter/flutter/issues/53789 Change-Id: I11eae4c99d73d91cd397e04730879abb8f394d20 Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/3121 Reviewed-by: Godofredo Contreras <godofredoc@google.com> Commit-Queue: Tong Wu <wutong@google.com>