Cloud Backup (BaaS) support

[tintoy]

Where practical, retain the semantics of the API as CloudControl provides it (rather than trying to provide an abstraction / application-level error handling as part of the client).

• [ ] Expose backup status on Server struct.

APIs:

• [x] Backup service
  • [x] Enable Backup for a Server
  • [x] Disable Backup for a Server
  • [x] Change Backup Service
• [ ] Backup clients
  • [x] Get Backup Client Types
  • [ ] Add Backup Client
  • [ ] Remove Backup Client
  • [ ] Modify Backup Client
  • [ ] Cancel Jobs for Backup Client
• [x] Policies
  • [x] Get Storage Policies
  • [x] Get Schedule Policies

Additionally:

• [x] Unit tests
• [x] Integration tests
• [x] GoDoc comments