Take a list of element node indexes deliminated by -1 and convert
    it into a list element node indexes list.

def _convertToElementList(elements_list):
    """
    Take a list of element node indexes deliminated by -1 and convert
    it into a list element node indexes list.
    """
    elements = []
    current_element = []
    for node_index in elements_list:
        if node_index == -1:
            elements.append(current_element)
            current_element = []
        else:
            current_element.append(node_index)

    return elements