Make it pass CECT 11.1.3 System standby

- Accept the broadcast <Standby> message.
- Fix the bug that onStandyCompleted() is called mutliple times.
- Fix the issue that <Standby> message is not sent when going to
  the standby state, since the local device was cleared already.

Bug: 16497304
Change-Id: Ib04ad2386621929814a801edd6b6c0e1a3902a7c