Conform response for grouping query to api design

@abersager
@maxfliri

backdrop/core/bucket.py

@@ -39,7 +39,8 @@ def execute_weekly_group_query(self, key2, query):
 
     def execute_grouped_query(self, group_by, query):
         cursor = self.repository.group(group_by, query)
-        result = [{doc[group_by]: doc['_count']} for doc in cursor]
+        result = [{group_by: doc[group_by], '_count': doc['_count']} for doc
+                  in cursor]
         return result
 
     def execute_period_query(self, query):

features/read_api.feature

@@ -46,22 +46,22 @@ Feature: the performance platform read api
          when I go to "/foo?group_by=authority"
          then I should get back a status of "200"
           and the JSON should have "2" results
-          and the "1st" result should be "{"Westminster": 4}"
-          and the "2nd" result should be "{"Camden": 2}"
+          and the "1st" result should be "{"authority": "Westminster", "_count": 4}"
+          and the "2nd" result should be "{"authority": "Camden", "_count": 2}"
 
     Scenario: extracting data for a representation
         Given "licensing_2.json" is in "foo" bucket
          when I go to "/foo?group_by=authority&filter_by=licence_name:Temporary%20events%20notice"
          then I should get back a status of "200"
           and the JSON should have "2" results
-          and the "1st" result should be "{"Westminster": 3}"
+          and the "1st" result should be "{"authority": "Westminster", "_count": 3}"
 
         Given "licensing_2.json" is in "foo" bucket
          when I go to "/foo?group_by=licence_name&filter_by=authority:Westminster"
          then I should get back a status of "200"
           and the JSON should have "2" results
-          and the "1st" result should be "{"Temporary events notice": 3}"
-          and the "2nd" result should be "{"Cat herding licence": 1}"
+          and the "1st" result should be "{"licence_name": "Temporary events notice", "_count": 3}"
+          and the "2nd" result should be "{"licence_name": "Cat herding licence", "_count": 1}"
 
     Scenario: invalid request parameters
          When I go to "/foo?start_at=not+a+date"

tests/core/test_bucket.py

@@ -57,9 +57,11 @@ def test_group_by_query(self):
         self.mock_repository.group.assert_called_once_with("name", {})
 
         assert_that(query_result,
-                    has_item(has_entries({'Max': equal_to(3)})))
+                    has_item(has_entries({'name': equal_to('Max'),
+                                          '_count': equal_to(3)})))
         assert_that(query_result,
-                    has_item(has_entries({'Gareth': equal_to(2)})))
+                    has_item(has_entries({'name': equal_to('Gareth'),
+                                          '_count': equal_to(2)})))
 
     def test_query_with_start_at(self):
         self.bucket.query(start_at = d(2013, 4, 1, 12, 0, 0))