Test DNSRecordGetter with mock DNS

[AlexCarmel]

Currently we don't have any tests to test DNSRecordGetter. We can use PHPUnit Bridge from symphony framework to mock DNS records. To test dns_get_record we can use:

DnsMock::withMockedHosts(array(
    'example.com' => array(
        array(
            'type' => 'A',
            'ip' => '1.2.3.4',
        )
    ),
));

[Mika56]

I didn't know about this mock, I was looking at starting a Docker container with some DNS server, but this looks way easier :D Might take a look before the end of the week