After restart NM should resync with the RM without killing containers

After RM restart, the RM sends a resync response to NMs that heartbeat to it. Upon receiving the resync response, the NM kills all containers and re-registers with the RM. The NM should be changed to not kill the container and instead inform the RM about all currently running containers including their allocations etc. After the re-register, the NM should send all pending container completions to the RM as usual.