SHDP-439 Add support for graceful yarn app shutdown

- First stage changes
- This now brings a base support for allowing boot based
  yarn app to shut itself down. Configuration is not yet
  fully automated in terms of auto-configuration but
  allows you to define custom beans on your app side
  to do shutdown cleanly.
- Add ContainerShutdown interface to allow external beans
  to shutdown containers.
- Add YarnContainerRegisterMvcEndpoint which container
  can use to register itself i.e. telling its
  shutdown boot endpoint.
- Add YarnShutdownCommand which can use boot shutdown
  endpoint to tell appmaster to go down.
- Second stage brings more auto-configuration changes
  to make things easier.