resolve KeyError: 'PDSH_SSH_ARGS_APPEND' (#5318)
when start job with `deepspeed --hostfile hostfile --master_addr
$MASTER_IP --ssh_port 20023 src/train_bash.py `
get error: KeyError: 'PDSH_SSH_ARGS_APPEND' in
https://github.com/microsoft/DeepSpeed/blob/master/deepspeed/launcher/multinode_runner.py#L77
because PDSH_SSH_ARGS_APPEND not in environment.
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Co-authored-by: Logan Adams <114770087+loadams@users.noreply.github.com>
