Make docker distribution CUD asynchronous

[asmacdo]

Creates functional tests based on regular distributions. Comment out
some failing tests which check functionality that is broken.

https://pulp.plan.io/issues/4582
fixes #4582

[pep8speaks]

Hello @asmacdo! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-04-03 13:28:16 UTC

[ipanova]

(pulp) [vagrant@pulp3-source-fedora29 pulp_docker]$ http POST http://localhost:8000/pulp/api/v3/docker-distributions/ name='baz' base_path='foo' publication=/pulp/api/v3/publications/1820ddf0-003c-47c2-adbc-2cf573e73dd3/
HTTP/1.1 202 Accepted
Allow: GET, POST, DELETE, HEAD, OPTIONS
Connection: close
Content-Length: 67
Content-Type: application/json
Date: Mon, 01 Apr 2019 14:49:03 GMT
Server: gunicorn/19.9.0
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

{
    "task": "/pulp/api/v3/tasks/dc3274b8-dc90-472a-8e1b-5159802f9fd9/"
}

(pulp) [vagrant@pulp3-source-fedora29 pulp_docker]$ http GET  :8000/pulp/api/v3/tasks/dc3274b8-dc90-472a-8e1b-5159802f9fd9/
HTTP/1.1 200 OK
Allow: GET, DELETE, HEAD, OPTIONS
Connection: close
Content-Length: 523
Content-Type: application/json
Date: Mon, 01 Apr 2019 14:49:11 GMT
Server: gunicorn/19.9.0
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

{
    "_created": "2019-04-01T14:49:03.187703Z",
    "_href": "/pulp/api/v3/tasks/dc3274b8-dc90-472a-8e1b-5159802f9fd9/",
    "created_resources": [
        "/pulp/api/v3/docker-distributions/286a2335-dee7-4cbb-8423-77951dda728b/"
    ],
    "error": null,
    "finished_at": "2019-04-01T14:49:03.440485Z",
    "name": "pulp_docker.app.tasks.distribution.create",
    "non_fatal_errors": [],
    "parent": null,
    "progress_reports": [],
    "spawned_tasks": [],
    "started_at": "2019-04-01T14:49:03.347621Z",
    "state": "completed",
    "worker": "/pulp/api/v3/workers/89b26d22-c106-47e2-b47e-fe4b1bbd1441/"
}

(pulp) [vagrant@pulp3-source-fedora29 pulp_docker]$ http GET  :8000/pulp/api/v3/docker-distributions/286a2335-dee7-4cbb-8423-77951dda728b/
HTTP/1.1 200 OK
Allow: GET, PUT, PATCH, DELETE, HEAD, OPTIONS
Connection: close
Content-Length: 342
Content-Type: application/json
Date: Mon, 01 Apr 2019 14:50:30 GMT
Server: gunicorn/19.9.0
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

{
    "_created": "2019-04-01T14:49:03.428024Z",
    "_href": "/pulp/api/v3/docker-distributions/286a2335-dee7-4cbb-8423-77951dda728b/",
    "base_path": "foo",
    "content_guard": null,
    "name": "baz",
    "publication": "/pulp/api/v3/publications/1820ddf0-003c-47c2-adbc-2cf573e73dd3/",
    "publisher": null,
    "registry_path": "localhost:8080/foo",
    "remote": null,
    "repository": null
}