Generates Node message from params and system information.

def get_node(service_name, host_name):
    """Generates Node message from params and system information.
    """
    return common_pb2.Node(
        identifier=common_pb2.ProcessIdentifier(
            host_name=socket.gethostname() if host_name is None
            else host_name,
            pid=os.getpid(),
            start_timestamp=proto_ts_from_datetime(
                datetime.datetime.utcnow())),
        library_info=common_pb2.LibraryInfo(
            language=common_pb2.LibraryInfo.Language.Value('PYTHON'),
            exporter_version=EXPORTER_VERSION,
            core_library_version=opencensus_version),
        service_info=common_pb2.ServiceInfo(name=service_name))