suppose am work preserving and rm ha is enabled.
container complete message is passed to appattemt.justFinishedContainers in rm。in normal situation，all attempt in one app shares the same justFinishedContainers, but when rm changed, every attempt has it's own justFinishedContainers, so in situations below, container complete message couldn't passed to am:
1, am restart
2, rm changes
3, container launched by first am completes
container complete message will be passed to appAttempt1 not appAttempt2, but am pull finished containers from appAttempt2 (currentAppAttempt)