Takes a number of parameters used when starting a jobflow (as
        specified in run_jobflow() above). Returns a comparable dict for
        use in making a RunJobFlow request.

def _build_instance_common_args(self, ec2_keyname, availability_zone,
                                    keep_alive, hadoop_version):
        """
        Takes a number of parameters used when starting a jobflow (as
        specified in run_jobflow() above). Returns a comparable dict for
        use in making a RunJobFlow request.
        """
        params = {
            'Instances.KeepJobFlowAliveWhenNoSteps' : str(keep_alive).lower(),
        }

        if hadoop_version:
            params['Instances.HadoopVersion'] = hadoop_version
        if ec2_keyname:
            params['Instances.Ec2KeyName'] = ec2_keyname
        if availability_zone:
            params['Instances.Placement.AvailabilityZone'] = availability_zone

        return params