get enviroment variables for slaves
        can be passed in as args or envs

def slave_envs(self):
        """
        get enviroment variables for slaves
        can be passed in as args or envs
        """
        if self.hostIP == 'dns':
            host = socket.gethostname()
        elif self.hostIP == 'ip':
            host = socket.gethostbyname(socket.getfqdn())
        else:
            host = self.hostIP
        return {'rabit_tracker_uri': host,
                'rabit_tracker_port': self.port}