class_docstr: tracker for rabit
class_docstr_tok: ["tracker","for","rabit"]
docstr: get enviroment variables for slaves
  can be passed in as args or envs
docstr_tok: ["get","enviroment","variables","for","slaves","can","be","passed","in","as","args","or","envs"]
code: def slave_envs(self):
      """
      get enviroment variables for slaves
      can be passed in as args or envs
      """
      return {
          "DMLC_TRACKER_URI": self.hostIP,
          "DMLC_TRACKER_PORT": self.port,
      }
  
imports: from __future__ import absolute_import
  import os
  import sys
  import socket
  import struct
  import subprocess
  import argparse
  import time
  import logging
  from threading import Thread
label_desc: Use image node_id 4 for calling the RabitTracker obj's underlying member method code with example usage: obj.slave_envs() and returns: dict