Discover DNS Information

Similar to https://blueprints.launchpad.net/satori/+spec/poc-certificate-detection.

For a given netloc, fetch and parse the DNS information. Probable fields to populate are:

Domain
Expiration date
Nameservers
Registrar
Whois Text
Errors

Building off of https://blueprints.launchpad.net/satori/+spec/nova-instance-detection, the command line output would gain a DNS line:

$ satori www.foo.com
Address:
   www.foo.com resolves to IPv4 address 4.4.4.4
DNS:
  foo.com expires on 2016-01-01 (745 days)
  Authoritative nameservers: dns1.example.com, dns2.example.com

Python example:
>>> import satori
>>>satori.discover(address='https://www.foo.com')
{
 'dns': {
  'domain': 'foo.com',
  'expiration-date': datetime.date(2016, 1, 1),
  'nameservers': ['dns1.example.com', 'dns2.example.com'],
  'erorrs': []
 }
}