[WIP]Added a test for a complete request/response,Issue #13

Hello! 

We tried to write a test for Issue #13 ( @dionyziz ). Previous tests mocked: 
'dnschain.server.urllib.FancyURLopener'
which was not imported in dnschain.server, so they failed. For that, we changed "urllib.FancyURLopener" to "urllib2.urlopen", which is what dnschain.server uses. 

If you do not agree with this change, let us know, so as to revert it :) . 

Let us know if there is anything you want us to change or add.