-d option errors if IP address is passed

[joekir]

I hadn't used the tool before and was trying a few options. I incorrectly used an IP address with the domain flag option. It errored far into the code away from the input parsing, due to line 1415 of dnsrecon.py not validating the input format.

 elif opt in ('-d', '--domain'):
            domain = arg

I think it would be good to refactor this section to use argparse.

[darkoperator]

Thanks for the tip, will need to thing what is the best ways