Update ddns.py

[clia]

对*子域名记录的DNS解析进行特殊处理

[rfancn]

Thanks for your PR, the way to set a non-existed subdomain when find "*" subdomain is great. My comments is below:

• it is possible that user already have a "xxx." record, and syncd IP for such domain record before, in this case, it will not update the remote record as we expected because it saw that IP for xxx.domain didn't get changed
• the better place to check for "*" subdomain should be in utils.get_dns_resolved_ip(), as specific "@" subdomain also handled there

Base on above, I changed your codes to generate a 12 character random fake subdomain in utils.get_dns_resolved_ip() when handling "*" subdomain, hopefully the subdomain clashes probability should be highly reduced though we cannot guarantee 100% no clashes.