This is related to  bug 800059 .  When the bad directory
that couldn't be offloaded was encountered, the behavior
of gs_offloader was to terminate, and write an exception
like this _to stderr_:
Traceback (most recent call last):
  File "/usr/local/autotest/site-packages/chromite/lib/parallel.py", line 603, in TaskRunner
    task(*x, **task_kwargs)
  File "/usr/local/autotest/site-packages/chromite/lib/metrics.py", line 483, in wrapper
    return fn(*args, **kwargs)
  File "/usr/local/autotest/site_utils/gs_offloader.py", line 581, in offload
    stderr_file)
  File "/usr/local/autotest/site_utils/gs_offloader.py", line 627, in _offload
    sanitize_dir(dir_entry)
  File "/usr/local/autotest/site_utils/gs_offloader.py", line 208, in sanitize_dir
    _escape_rename_dir_contents(dirpath)
  File "/usr/local/autotest/site_utils/gs_offloader.py", line 224, in _escape_rename_dir_contents
    _escape_rename_dir_contents(path)
  File "/usr/local/autotest/site_utils/gs_offloader.py", line 224, in _escape_rename_dir_contents
    _escape_rename_dir_contents(path)
  File "/usr/local/autotest/site_utils/gs_offloader.py", line 224, in _escape_rename_dir_contents
    _escape_rename_dir_contents(path)
  File "/usr/local/autotest/site_utils/gs_offloader.py", line 224, in _escape_rename_dir_contents
    _escape_rename_dir_contents(path)
  File "/usr/local/autotest/site_utils/gs_offloader.py", line 224, in _escape_rename_dir_contents
    _escape_rename_dir_contents(path)
  File "/usr/local/autotest/site_utils/gs_offloader.py", line 218, in _escape_rename_dir_contents
    for filename in os.listdir(dirpath):
OSError: [Errno 13] Permission denied: 'hosts/chromeos6-row3-rack11-host11/1699958-provision/20180901052429/crashinfo.chromeos6-row3-rack11-host11/var/log/dp

This isn't an acceptable failure mode:  No single job offload failure
should terminate gs_offloader.  The standard response to that sort
of event is supposed to be "log it and move on".

We need to adjust the offload loop so that there's a try block
at the highest level of the call chain for each individual directory.
That try block should implement the "log it and move on policy".