better assertEqual for dnspython

better assertEqual for dnspython

before:
AssertionError: <DNS message, ID 38993> != <DNS message, ID 38993>

after:
AssertionError: <DNS message, ID 46818> != <DNS message, ID 46818>:
--- first
+++ second
@@ -1,10 +1,10 @@
 id 46818
-opcode 6
-rcode NOTAUTH
-flags AD CD
+opcode QUERY
+rcode NOERROR
+flags RD
 ;QUESTION
 xpf.tests.powerdns.com. IN A
 ;ANSWER
 ;AUTHORITY
 ;ADDITIONAL
-. 0 IN TYPE65422 \# 14 04117f0000017f000001f8bc14dc
+xpf.tests.powerdns.com. 60 IN TYPE65422 \# 14 04117f0000017f00000100000000