Docker Support

While syncing docker content to repo, pulp fails at the first step of 'donwload manifest', the error log is as below. It seems like that the first download attempt failed and it's retrying, but I'm not sure. Since we have never seen it before, I wonder if it's a newly introduced bug.

Pulp task [f02a90b6-54aa-4b2a-bb2f-2a3c226b1248] failed: PLP0000: unsupported operand type(s) for -=: 'Retry' and 'int':
  Traceback (most recent call last):
    File "/usr/lib/python2.7/site-packages/celery/app/trace.py", line 367, in trace_task
      R = retval = fun(*args, **kwargs)
    File "/usr/lib/python2.7/site-packages/pulp/server/async/tasks.py", line 529, in __call__
      return super(Task, self).__call__(*args, **kwargs)
    File "/usr/lib/python2.7/site-packages/pulp/server/async/tasks.py", line 107, in __call__
      return super(PulpTask, self).__call__(*args, **kwargs)
    File "/usr/lib/python2.7/site-packages/celery/app/trace.py", line 622, in __protected_call__
      return self.run(*args, **kwargs)
    File "/usr/lib/python2.7/site-packages/pulp/server/controllers/repository.py", line 769, in sync
      sync_report = sync_repo(transfer_repo, conduit, call_config)
    File "/usr/lib/python2.7/site-packages/pulp/server/async/tasks.py", line 737, in wrap_f
      return f(*args, **kwargs)
    File "/usr/lib/python2.7/site-packages/pulp_docker/plugins/importers/importer.py", line 85, in sync_repo
      return self.sync_step.process_lifecycle()
    File "/usr/lib/python2.7/site-packages/pulp/plugins/util/publish_step.py", line 572, in process_lifecycle
      super(PluginStep, self).process_lifecycle()
    File "/usr/lib/python2.7/site-packages/pulp/plugins/util/publish_step.py", line 163, in process_lifecycle
      step.process()
    File "/usr/lib/python2.7/site-packages/pulp/plugins/util/publish_step.py", line 256, in process
      self._process_block()
    File "/usr/lib/python2.7/site-packages/pulp/plugins/util/publish_step.py", line 303, in _process_block
      self.process_main()
    File "/usr/lib/python2.7/site-packages/pulp_docker/plugins/importers/sync.py", line 224, in process_main
      available_tags = self.parent.index_repository.get_tags()
    File "/usr/lib/python2.7/site-packages/pulp_docker/plugins/registry.py", line 473, in get_tags
      headers, tags = self._get_path(link)
    File "/usr/lib/python2.7/site-packages/pulp_docker/plugins/registry.py", line 528, in _get_path
      self._raise_path_error(report)
    File "/usr/lib/python2.7/site-packages/pulp_docker/plugins/registry.py", line 550, in _raise_path_error
      raise IOError(report.error_msg)
  IOError: unsupported operand type(s) for -=: 'Retry' and 'int'