Add a chain to test records with a specified zone file

I have added to test records with a specified zone file. This makes us possible to test records before serving on dns servers.

```ruby
  it 'checks zone file("example.zone") with specified origin("example.com.")' do
    expect('example.com').to have_dns.with_type('A').zone_file('example.zone', 'example.com.')
  end
```

```ruby
  it 'checks zone file("example.zone") without specified origin' do
    expect('example.com').to have_dns.with_type('A').zone_file('example.zone')
  end
```