DNSDB Python3 Support

[milesflo]

These are the changes ported over from #607 that allow DNSDB to work on Python3.

Works on my machine but please test extensively as the vendor lib was upgraded by https://github.com/guyddr/dnsdb-query (a 3rd party).

[dadokkio]

Hi, I'm trying your analyzer but I don't know why my apy key [community edition trial] is working only few times and then returns error.

In any case when api fails it returns "Error: Bad API key" and then the analyzer fails with the following error [at line 119 when it tries to parse the error as json]:

Can you please check if the response is 200 before trying to parse it?

[dadokkio]

Ok, it wasn't the not 200 response but all the responses return error.

I think the problem [in dnsdb.py] is:

            self.report({
                "records": map(lambda r: self.update_date('time_first', self.update_date('time_last', r)),
                               self.execute_dnsdb_service(client))
            })

because map is an iterable and cannot be serialized.
If I add list to the code in this way:

            self.report({
                "records": list(map(lambda r: self.update_date('time_first', self.update_date('time_last', r)),
                               self.execute_dnsdb_service(client)))
            })

it seems to be working.

[garanews]

merged the #745