Container leak on NM

Caused by YARN-1372. thanks vinodkv for pointing this out.

The problem is that in YARN-1372 we changed the behavior to remove containers from NMContext only after the containers are acknowledged by AM. But in the NodeStatusUpdaterImpl#removeCompletedContainersFromContext call, we didn't check whether the container is really completed or not. If the container is stilll running, we shouldn't remove the container from the context