Docker Support

When I tried
curl -X POST https://pulp-dev:443/pulp/api/v2/repositories/1a18d18e-b20e-471d-baa2-6aa108941122/actions/sync/ --data '{"override_config": {"feed": "https://registry-1.docker.io", "upstream_name": "busybox", "ssl_validation": false, "enable_v1": true}}'

Sync task failed with

PulpException: Could not fetch repository busybox from registry https://registry-1.docker.io - METHOD NOT ALLOWED DKR1007
Traceback (most recent call last):
File "/usr/lib/python2.7/site-packages/celery/app/trace.py", line 240, in trace_task
R = retval = fun(*args, **kwargs)
File "/home/vagrant/devel/pulp/server/pulp/server/async/tasks.py", line 488, in call
return super(Task, self).__call__(*args, **kwargs)
File "/home/vagrant/devel/pulp/server/pulp/server/async/tasks.py", line 103, in call
return super(PulpTask, self).__call__(*args, **kwargs)
File "/usr/lib/python2.7/site-packages/celery/app/trace.py", line 438, in protected_call
return self.run(*args, **kwargs)
File "/home/vagrant/devel/pulp/server/pulp/server/controllers/repository.py", line 760, in sync
sync_report = sync_repo(transfer_repo, conduit, call_config)
File "/home/vagrant/devel/pulp/server/pulp/server/async/tasks.py", line 673, in wrap_f
return f(*args, **kwargs)
File "/home/vagrant/devel/pulp_docker/plugins/pulp_docker/plugins/importers/importer.py", line 84, in sync_repo
return self.sync_step.process_lifecycle()
File "/home/vagrant/devel/pulp/server/pulp/plugins/util/publish_step.py", line 565, in process_lifecycle
super(PluginStep, self).process_lifecycle()
File "/home/vagrant/devel/pulp/server/pulp/plugins/util/publish_step.py", line 162, in process_lifecycle
step.process()
File "/home/vagrant/devel/pulp/server/pulp/plugins/util/publish_step.py", line 252, in process
self._process_block()
File "/home/vagrant/devel/pulp/server/pulp/plugins/util/publish_step.py", line 296, in _process_block
self.process_main()
File "/home/vagrant/devel/pulp_docker/plugins/pulp_docker/plugins/importers/v1_sync.py", line 51, in process_main
available_images = self.parent.v1_index_repository.get_image_ids()
File "/home/vagrant/devel/pulp_docker/plugins/pulp_docker/plugins/registry.py", line 166, in get_image_ids
reason=str(e))
PulpCodedException: Could not fetch repository busybox from registry https://registry-1.docker.io - METHOD NOT ALLOWED

but docker pull
$ docker pull busybox
latest: Pulling from docker.io/busybox
4185ddbe03f8: Pull complete
b05baf071fd5: Pull complete
Digest: sha256:65ce39ce3eb0997074a460adfb568d0b9f0f6a4392d97b6035630c9d7bf92402
Status: Downloaded newer image for docker.io/busybox:latest

worked