tests: add dnspython from git into requirements

tests-extra/README

@@ -11,6 +11,12 @@ lsof
 (valgrind)
 (gdb)
 
+Python modules:
+---------------
+
+To install necessary Python modules using pip, run:
+$ pip install -r requirements.txt
+
 Ubuntu:
 -------
 Disable apparmor protection for system Bind:

tests-extra/requirements.txt

-dnspython3==1.11.1
+#dnspython3==1.11.1
+-e git+https://github.com/rthalley/dnspython.git@python3#egg=dnspython3
 psutil==1.2.1