Description of problem:
When creating authentications using /api/authentications the action fails with undefined method `id' for nil:NilClass


Version-Release number of selected component (if applicable):
5.8.1.5


How reproducible:
very


Steps to Reproduce:
1.
POST /api/authentications
{
  "description" : "Authentication Description1",
  "name" : "SomeCredentials1",
  "related" : {},
  "type" : "ManageIQ::Providers::AnsibleTower::AutomationManager::Credential",
  "manager_resource" : { "href" : "https://<address>/api/providers/:id_of_ansible_provider" }
}
2. check corresponding task


Actual results:
{
...
    "name": "Creating Ansible Tower Credential (name=SomeCredentials1)",
    "state": "Finished",
    "status": "Error",
    "message": "undefined method `id' for nil:NilClass",
    "userid": "system",
...
}


Expected results:
Authentication is created