Support speculative execution on YARN for straggler task

[zhangpengshan]

For MapReduce version, we cannot enable speculative execution because we cannot control which task need to be enabled speculative execution. It is based on mapper progress while mapper progress is almost the same and once some task is proved to be faster, such speculative task attempt should be killed. It is hard in MapReduce.

In YARN, we have the freedom to do that, to build specific speculative mechanism.