[FLINK-1154] Quickfix to kill TaskManagers in YARN mode.

This quickfix should probably only go into the 0.7 branch for the 0.7.1 release since the new Akka-based JM/TMs have this issue fixed.
I would strongly vote to remove that. There is no need to kill a TaskManager just because it lost its heartbeat. The TaskManager may very well reconnect later and be available again.