REST API Enhancement to support Automation Requests

    REST API Enhancement to support Automation Requests
    
    - new /api/automation_requests
    - support POST (create requests) and GET (query requests)
    - support /api/automation_requests/#/request_tasks subcollection.
    - support /api/automation_requests/#/tasks subcollection.

Note: Depends on https://github.com/ManageIQ/manageiq/pull/260