Validate that the specified property names are indeed defined on the given class.

def validate_properties_exist(self, classname, property_names):
        """Validate that the specified property names are indeed defined on the given class."""
        schema_element = self.get_element_by_class_name(classname)

        requested_properties = set(property_names)
        available_properties = set(schema_element.properties.keys())
        non_existent_properties = requested_properties - available_properties
        if non_existent_properties:
            raise InvalidPropertyError(
                u'Class "{}" does not have definitions for properties "{}": '
                u'{}'.format(classname, non_existent_properties, property_names))