SHDP-266 Better exit code handling

- Add better handling for return value
  of pojo method run from boot model.
- Pojo return value as String can now
  map back to generic launcher exit codes.
- Added DefaultYarnContainer to instruct
  ContainerLauncherRunner to wait state.
- ContainerStateListener changed to use Object
  as exit status instead of int. This way we
  can do better mapping.