Providers API

GET    /api/v1/providers              # List
POST   /api/v1/providers              # Create
GET    /api/v1/providers/{id}         # Get
PUT    /api/v1/providers/{id}         # Update
DELETE /api/v1/providers/{id}         # Delete
POST   /api/v1/providers/{id}/test    # Test connection
GET    /api/v1/providers/{id}/regions # List regions
GET    /api/v1/providers/{id}/sizes   # List instance types