File Support

Followed the README instructions for creating the `foo` repository, and hit an error on the second step, 'Add and Importer to Repository foo'.

The 'foo' repository created successfully, and returned the following:

HTTP/1.0 201 Created
Allow: GET, POST, HEAD, OPTIONS
Content-Length: 338
Content-Type: application/json
Date: Fri, 08 Dec 2017 10:14:43 GMT
Location: http://localhost:8000/api/v3/repositories/15e6265c-866b-469a-bcbf-7f2f1535aaa3/
Server: WSGIServer/0.2 CPython/3.6.1
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

{
    "_href": "http://localhost:8000/api/v3/repositories/15e6265c-866b-469a-bcbf-7f2f1535aaa3/",
    "content": "http://localhost:8000/api/v3/repositories/15e6265c-866b-469a-bcbf-7f2f1535aaa3/content/",
    "content_summary": {},
    "description": "",
    "importers": [],
    "last_content_added": null,
    "last_content_removed": null,
    "name": "foo",
    "notes": {},
    "publishers": []
}

The next request "http POST http://localhost:8000/api/v3/repositories/foo/importers/file/ name='bar' download_policy='immediate' sync_mode='mirror' feed_url='https://repos.fedorapeople.org/pulp/pulp/demo_repos/test_file_repo/PULP_MANIFEST'" failed with the following response:

HTTP/1.0 404 Not Found
Allow: GET, POST, HEAD, OPTIONS
Content-Length: 23
Content-Type: application/json
Date: Fri, 08 Dec 2017 10:15:26 GMT
Server: WSGIServer/0.2 CPython/3.6.1
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

{
    "detail": "Not found."
}

Substituting 'foo' with the Id of the repository worked. I changed the request to "http POST http://localhost:8000/api/v3/repositories/15e6265c-866b-469a-bcbf-7f2f1535aaa3/importers/file/ name='bar' download_policy='immediate' sync_mode='mirror' feed_url='https://repos.fedorapeople.org/pulp/pulp/demo_repos/test_file_repo/PULP_MANIFEST'", and it worked, giving the following response:

HTTP/1.0 201 Created
Allow: GET, POST, HEAD, OPTIONS
Content-Length: 494
Content-Type: application/json
Date: Fri, 08 Dec 2017 10:16:57 GMT
Location: http://localhost:8000/api/v3/repositories/15e6265c-866b-469a-bcbf-7f2f1535aaa3/importers/file/bar/
Server: WSGIServer/0.2 CPython/3.6.1
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

{
    "_href": "http://localhost:8000/api/v3/repositories/15e6265c-866b-469a-bcbf-7f2f1535aaa3/importers/file/bar/",
    "download_policy": "immediate",
    "feed_url": "https://repos.fedorapeople.org/pulp/pulp/demo_repos/test_file_repo/PULP_MANIFEST",
    "last_synced": null,
    "last_updated": "2017-12-08T10:16:57.284111Z",
    "name": "bar",
    "proxy_url": "",
    "repository": "http://localhost:8000/api/v3/repositories/15e6265c-866b-469a-bcbf-7f2f1535aaa3/",
    "ssl_validation": true,
    "sync_mode": "mirror",
    "type": "file",
    "validate": true
}