Exclude online nntp tests from tox conf

tox.ini

@@ -18,9 +18,9 @@ setenv =
 
 commands =
     coverage erase
-    coverage run manage.py test -v 2
-    coverage report --include='debexpo*'
-    coverage html --include='debexpo*'
+    coverage run manage.py test -v 2 --exclude-tag nntp
+    coverage report --include='debexpo*' --omit '*/nntp.py'
+    coverage html --include='debexpo*' --omit '*/nntp.py'
 
 [testenv:flake8]
 deps = flake8