Don't test epoch values against naive datetimes

When running the test suite on a machine set to the UTC timezone,
`test_find_timestamp` would fail, because the datetime object used to
seed the value is timezone-naive.  The test would work fine in UTC+1
timezones, but not in other timezones.

tests/unittests/general/prefix_ip_collector_test.py

@@ -3,7 +3,7 @@
 """Tests for prefix_ip_collector"""
 
 import unittest
-from datetime import datetime
+from datetime import datetime, timezone
 from nav.activeipcollector.manager import find_range, get_timestamp
 
 
@@ -14,5 +14,5 @@ def test_find_range(self):
         self.assertEqual(find_range('2001:700:0:251e::/64'), 0)
 
     def test_find_timestamp(self):
-        ts = datetime(2012, 10, 4, 14, 30)
-        self.assertEqual(get_timestamp(ts), 1349353800)
+        ts = datetime(2012, 10, 4, 14, 30, tzinfo=timezone.utc)
+        self.assertEqual(get_timestamp(ts), 1349361000)