Test - Few fields returned by task reported by orphans endpoint set as None

[fao89]

Author: kersom (kersom)

Redmine Issue: 5255, https://pulp.plan.io/issues/5255

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Task returned by the orphans endpoint as completed, but a few fields ( finished_at, started_at, worker) are set as None.

{'_created': '2018-12-21T00:26:37.278392Z',
 '_href': '/pulp/api/v3/tasks/b963e89c-db1a-4db4-b8c9-5fbca5629113/',
 'created_resources': [],
 'error': None,
 'finished_at': None,
 'name': 'pulpcore.app.tasks.orphan.orphan_cleanup',
 'non_fatal_errors': [],
 'parent': None,
 'progress_reports': [{'done': 3,
                       'message': 'Clean up orphan Content',
                       'state': 'completed',
                       'suffix': '',
                       'task': '/pulp/api/v3/tasks/b963e89c-db1a-4db4-b8c9-5fbca5629113/',
                       'total': 3},
                      {'done': 3,
                       'message': 'Clean up orphan Artifacts',
                       'state': 'completed',
                       'suffix': '',
                       'task': '/pulp/api/v3/tasks/b963e89c-db1a-4db4-b8c9-5fbca5629113/',
                       'total': 3}],
 'spawned_tasks': [],
 'started_at': None,
 'state': 'completed',
 'worker': None}

Pulp 3 installation from source. April/09.