'Fill in  controller task parameters.
Returned parameters map is to be used as task payload, and it contains
all the data, required by controller to perform its function.
Args:
mapreduce_spec: specification of the mapreduce.
serial_id: id of the invocation as int.
Returns:
string->string map of parameters to be used as task payload.'

@staticmethod
def controller_parameters(mapreduce_spec, serial_id):

    return {'mapreduce_spec': mapreduce_spec.to_json_str(), 'serial_id': str(serial_id)}
