'Takes a master instance type (string), a slave instance type
(string), and a number of instances. Returns a comparable dict
for use in making a RunJobFlow request.'

def _build_instance_count_and_type_args(self, master_instance_type, slave_instance_type, num_instances):

    params = {'Instances.MasterInstanceType': master_instance_type, 'Instances.SlaveInstanceType': slave_instance_type, 'Instances.InstanceCount': num_instances}
    return params
