When trying to isolate a directory that contains broken symlinks, isolate.py will either:
- fail early if --ignore_broken_items is not set
- skip the entire directory if --ignore_broken_items is set

In the 2nd option, would it not make more sense to isolate what isn't broken? As it is, it skips the entire directory even if it contains valid files. I think a best effort approach to isolating the directory would be more appropriate.