Refactor DNSBL instance setup and add query patch
Refactor DNSBL instance setup and add query patch

New code responsible for creating DNSBL instance for tests in DNSBLTest class uses
a separate class method: setUpDNSBLInstance(code_item_class, query_suffix).

Patching query function (which was imported  from dns.resolver) in spambl module
is implemented in setUpQueryPatch(return_codes, existent_addr_suffix) and
tearDownClass class methods.

setUpDNSBLInstance and setUpQueryPatch are both called by setUpClass method,
and they receive their arguments from it.

piotr-rusin/spam-lists