'Open and parse an xml file.
TODO: Write custom parser to just read the nodes that we need instead
of reading the whole file.
@return xml_tree An xml tree instance. None if error.'

def parse_xml(self, xml_output):

    asset_data_report = '<!DOCTYPE    ASSET_DATA_REPORT    SYSTEM'
    scan_report = '<!DOCTYPE    SCAN    SYSTEM'
    try:
        tree = ET.fromstring(xml_output)
        if (asset_data_report in xml_output):
            type_report = 'ASSET_DATA_REPORT'
        elif (scan_report in xml_output):
            type_report = 'SCAN'
        else:
            type_report = None
    except SyntaxError as err:
        self.devlog(('SyntaxError:    %s.    %s' % (err, xml_output)))
        return (None, None)
    return (tree, type_report)
