Making unit_key a non-required field

[daviddavis]

None was a valid value for unit_key until a commit began requiring it.
This fixes the backward incompatible change.

fixes #3307
https://pulp.plan.io/issues/3307

[ipanova]

Before patch:

$ curl -k -u admin:admin -X POST -d '{"override_config": {}, "unit_type_id": "rpm", "upload_id": "3d5d089b-0e2d-4f1f-9a0e-be32a8bc1f60", "unit_key": null, "unit_metadata": {}}' https://localhost/pulp/api/v2/repositories/zoo/actions/import_upload/ -H "Content-Type: application/json"
{"spawned_tasks": [{"_href": "/pulp/api/v2/tasks/8efbb7b8-9ca3-4590-b21b-77683c25054f/", "task_id": "8efbb7b8-9ca3-4590-b21b-77683c25054f"}], "result": null, "error": null}[ipanova@ina pulp_rpm]$ 
[ipanova@ina pulp_rpm]$ 
[ipanova@ina pulp_rpm]$ $ pulp-admin -vv tasks details --task-id 8efbb7b8-9ca3-4590-b21b-77683c25054f

+----------------------------------------------------------------------+
                              Task Details
+----------------------------------------------------------------------+

2018-02-27 11:11:59,493 - DEBUG - sending GET request to /pulp/api/v2/tasks/8efbb7b8-9ca3-4590-b21b-77683c25054f/
2018-02-27 11:11:59,579 - INFO - GET request to /pulp/api/v2/tasks/8efbb7b8-9ca3-4590-b21b-77683c25054f/ with parameters None
2018-02-27 11:11:59,579 - INFO - Response status : 200 

2018-02-27 11:11:59,579 - INFO - Response body :
 {
  "exception": null, 
  "task_type": "pulp.server.managers.content.upload.import_uploaded_unit", 
  "_href": "/pulp/api/v2/tasks/8efbb7b8-9ca3-4590-b21b-77683c25054f/", 
  "task_id": "8efbb7b8-9ca3-4590-b21b-77683c25054f", 
  "tags": [
    "pulp:repository:zoo", 
    "pulp:action:import_upload"
  ], 
  "finish_time": "2018-02-27T10:11:49Z", 
  "_ns": "task_status", 
  "start_time": "2018-02-27T10:11:49Z", 
  "traceback": "Traceback (most recent call last):\n  File \"/usr/lib/python2.7/site-packages/celery/app/trace.py\", line 240, in trace_task\n    R = retval = fun(*args, **kwargs)\n  File \"/home/ipanova/pulp_development/pulp/server/pulp/server/async/tasks.py\", line 529, in __call__\n    return super(Task, self).__call__(*args, **kwargs)\n  File \"/home/ipanova/pulp_development/pulp/server/pulp/server/async/tasks.py\", line 107, in __call__\n    return super(PulpTask, self).__call__(*args, **kwargs)\n  File \"/usr/lib/python2.7/site-packages/celery/app/trace.py\", line 438, in __protected_call__\n    return self.run(*args, **kwargs)\n  File \"/home/ipanova/pulp_development/pulp/server/pulp/server/managers/content/upload.py\", line 223, in import_uploaded_unit\n    unit_type=unit_type_id, summary=result['summary'], details=result['details']\nPulpCodedException: The importer yum_importer indicated a failed response when uploading rpm unit to repository zoo.\n", 
  "spawned_tasks": [], 
  "progress_report": {}, 
  "queue": "reserved_resource_worker-0@ina.dq", 
  "state": "error", 
  "worker_name": "reserved_resource_worker-0@ina", 
  "result": null, 
  "error": {
    "code": "PLP0047", 
    "data": {
      "unit_type": "rpm", 
      "importer_id": "yum_importer", 
      "repo_id": "zoo", 
      "details": {
        "errors": [
          "unexpected error occurred importing uploaded file: 'NoneType' object has no attribute 'items'"
        ]
      }, 
      "summary": ""
    }, 
    "description": "The importer yum_importer indicated a failed response when uploading rpm unit to repository zoo.", 
    "sub_errors": []
  }, 
  "_id": {
    "$oid": "5a952ee51008f2b6763469c5"
  }, 
  "id": "5a952ee51008f2b6763469c5"
}

Operations:       import_upload
Resources:        zoo (repository)
State:            Failed
Start Time:       2018-02-27T10:11:49Z
Finish Time:      2018-02-27T10:11:49Z
Result:           N/A
Task Id:          8efbb7b8-9ca3-4590-b21b-77683c25054f
Progress Report:  
Traceback:        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/ipanova/pulp_development/pulp/server/pulp/server/async/
                  tasks.py", line 529, in __call__     return super(Task,
                  self).__call__(*args, **kwargs)   File
                  "/home/ipanova/pulp_development/pulp/server/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
                  438, in __protected_call__     return self.run(*args,
                  **kwargs)   File
                  "/home/ipanova/pulp_development/pulp/server/pulp/server/manage
                  rs/content/upload.py", line 223, in import_uploaded_unit    
                  unit_type=unit_type_id, summary=result['summary'],
                  details=result['details'] PulpCodedException: The importer
                  yum_importer indicated a failed response when uploading rpm
                  unit to repository zoo. 

After patch:

curl -k -u admin:admin -X POST -d '{"override_config": {}, "unit_type_id": "rpm", "upload_id": "11a92ebb-6344-43a7-8597-b04742fbf524", "unit_key": null, "unit_metadata": {}}' https://localhost/pulp/api/v2/repositories/zoo/actions/import_upload/ -H "Content-Type: application/json"
{"spawned_tasks": [{"_href": "/pulp/api/v2/tasks/21f98d0d-7219-4926-b65a-c88c600a608b/", "task_id": "21f98d0d-7219-4926-b65a-c88c600a608b"}], "result": null, "error": null}[ipanova@ina pulp_rpm]$ ^C
[ipanova@ina pulp_rpm] $ pulp-admin tasks details --task-id 21f98d0d-7219-4926-b65a-c88c600a608b
Warning: path should have mode 0700 because it may contain sensitive information: /home/ipanova/.pulp/

+----------------------------------------------------------------------+
                              Task Details
+----------------------------------------------------------------------+

Operations:       import_upload
Resources:        zoo (repository)
State:            Successful
Start Time:       2018-02-27T10:15:10Z
Finish Time:      2018-02-27T10:15:10Z
Result:           
  Details:      
  Success Flag: True
  Summary:      
Task Id:          21f98d0d-7219-4926-b65a-c88c600a608b
Progress Report: