generate type / spec Go code when spec is nil

[bradrydzewski]

abort and ignore types do not have a spec, however, the current Go code generator requires a target spec for all objects. Update the code generation to support this use case and then remove the failure_abort and failure_ignore schemas

oneOf:
- allOf:
  - properties:
      type:
        const: abort
  - properties:
      spec:
        $ref: ./failure_abort.yaml
- allOf:
  - properties:
      type:
        const: ignore
  - properties:
      spec:
        $ref: ./failure_ignore.yaml