And make sure that we return a schedule

Rather than just create it.

test/test_batch.py

@@ -0,0 +1,13 @@
+from unittest import TestCase
+from datetime import datetime
+
+from metrik.batch import flows
+
+
+class BatchTest(TestCase):
+    def test_flows_return_schedule(self):
+        present = datetime.now()
+        live = False
+        for flow_name, flow_class in flows.items():
+            assert flow_class(present=present,
+                              live=live).get_schedule() is not None