ONAP tracking of available external (ETSI compliant NFVO) orchestrators

An ONAP Service may be defined which needs to be deployed and managed by an external orchestrator.  This external orchestrator could be another instance of ONAP or an ETSI compliant NFVO. There may be many instances of external orchestrators with varying lifetimes.  In order for ONAP to deploy a service that requires an external orchestrator it needs to have a CRUD mechanism for external orchestrators with a description of functionality. The existing VF-C control could use this mechanism to register itself as an external ETSI compliant NFVO orchestrator.  Requirements:

1. Create, Read, Update, Delete Orchestrator instance functionality
   1. Data: URI, Creds, Region, Capabilities (ONAP, NFVO, ...), State, Health
2. List Orchestrator instances functionality
3. Test Orchestrator active & healthy functionality
4. Prevent deletion of an external orchestrator instance record if Service(s) that this external orchestrator instance deployed are still active.