Description of problem:
When creating new service via REST API the request fails when "parent_service" is "href" reference to existing service:
{
  "error": {
    "kind": "bad_request",
    "message": "Missing Service identifier id",
    "klass": "Api::BadRequestError"
  }
}

According to
http://manageiq.org/docs/reference/latest/api/reference/services#services
both "href" and "id" should be accepted.

Request is successful when "parent_service" is "id" reference to existing service.

Version-Release number of selected component (if applicable):
5.7.0.17

How reproducible:
100%

Steps to Reproduce:
1. create service
2. create service via REST API
POST /api/services
{
  "action" : "create",
  "resource" : {
    "name" : "test_service",
    "description" : "Test Service",
    "parent_service" : { "href" : "https://<address>/api/services/:id" }
  }
}