Clean up test warnings for Django 1.8

* Django 1.8 requires TEMPLATES setting (for admin tests)
* Ignore cycle tag deprecation warnings

One remaining PendingDeprecationWarning: "the imp module is
deprecated in favour of importlib" is coming from six, and has a fix
waiting to land: https://bitbucket.org/gutworth/six/issue/112

djrill/tests/test_admin.py

@@ -1,4 +1,5 @@
 import sys
+import warnings
 
 from django.test import TestCase
 from django.contrib.auth.models import User
@@ -9,6 +10,11 @@ from djrill.tests.mock_backend import DjrillBackendMockAPITestCase
 
 from .utils import override_settings
 
+# We don't care that the `cycle` template tag will be removed in Django 2.0,
+# because we're planning to drop the Djrill admin templates before then.
+warnings.filterwarnings('ignore', category=PendingDeprecationWarning,
+                        message="Loading the `cycle` tag from the `future` library")
+
 
 def reset_admin_site():
     """Return the Django admin globals to their original state"""