Set a label to span that can be used for tracing.
    :param span: Span object
    :param resource_type: resource type
    :param resource_labels: collection of labels
    :param attribute_key: actual label key
    :param canonical_key: exporter specific label key, Optional
    :param label_value_prefix: exporter specific label value prefix, Optional

def set_attribute_label(span, resource_type, resource_labels, attribute_key,
                        canonical_key=None, label_value_prefix=''):
    """Set a label to span that can be used for tracing.
    :param span: Span object
    :param resource_type: resource type
    :param resource_labels: collection of labels
    :param attribute_key: actual label key
    :param canonical_key: exporter specific label key, Optional
    :param label_value_prefix: exporter specific label value prefix, Optional
    """

    if attribute_key in resource_labels:
        if canonical_key is None:
            canonical_key = attribute_key

        pair = {RESOURCE_LABEL % (resource_type, canonical_key):
                label_value_prefix + resource_labels[attribute_key]
                }
        pair_attrs = Attributes(pair).format_attributes_json()\
            .get('attributeMap')

        _update_attr_map(span, pair_attrs)