Don't allow queries with 'IN' predicate with an empty sequence

While SQLalchemy-based storage tests running
(test_storage_scenarios.test_query_filter_with_empty_in) there was
invoked SAWarning: The IN-predicate on "sample.resource_id" with
an empty sequence.

Reason is in not checking of 'in' query lists elements number.
These queries make no sense, so JSON Schema for this was fixed.

Change-Id: I43ea2d20269c9567b3ef99936f63b7c0003170df

ceilometer/api/controllers/v2.py

@@ -1167,7 +1167,8 @@ class ValidatedComplexQuery(object):
         schema_value_in = {
             "type": "array",
             "items": {"oneOf": [{"type": "string"},
-                                {"type": "number"}]}}
+                                {"type": "number"}]},
+            "minItems": 1}
 
         schema_field = {
             "type": "object",

ceilometer/tests/api/v2/test_complex_query.py

@@ -392,3 +392,9 @@ class TestFilterSyntaxValidation(test.BaseTestCase):
         self.assertRaises(jsonschema.ValidationError,
                           self.query._validate_filter,
                           filter)
+
+    def test_empty_in_query_not_passing(self):
+        filter = {"in": {"resource_id": []}}
+        self.assertRaises(jsonschema.ValidationError,
+                          self.query._validate_filter,
+                          filter)

ceilometer/tests/storage/test_storage_scenarios.py

@@ -943,11 +943,6 @@ class ComplexSampleQueryTest(DBTestBase,
             self.assertTrue(sample.counter_volume > 0.4)
             self.assertTrue(sample.counter_volume <= 0.8)
 
-    def test_query_filter_with_empty_in(self):
-        results = list(
-            self.conn.query_samples(filter_expr={"in": {"resource_id": []}}))
-        self.assertEqual(len(results), 0)
-
     def test_query_simple_metadata_filter(self):
         self._create_samples()