Full response for DataProcessingClient methods

Since service clients need to be migrated to Tempest-lib, they should
not truncate any things from API response. Current DataProcessing client
cuts out the top key of a response and returns only value to the caller.
All service clients should return the response as they get it from APIs.

Change-Id: I0d2d47db0ccfb306269a60557c4e510082ad0d3e
Partially-implements: blueprint method-return-value-and-move-service-clients-to-lib
diff --git a/tempest/api/data_processing/test_data_sources.py b/tempest/api/data_processing/test_data_sources.py
index dd16b2f..67d09a0 100644
--- a/tempest/api/data_processing/test_data_sources.py
+++ b/tempest/api/data_processing/test_data_sources.py
@@ -68,13 +68,13 @@
 
     def _list_data_sources(self, source_info):
         # check for data source in list
-        sources = self.client.list_data_sources()
+        sources = self.client.list_data_sources()['data_sources']
         sources_info = [(source['id'], source['name']) for source in sources]
         self.assertIn(source_info, sources_info)
 
     def _get_data_source(self, source_id, source_name, source_body):
         # check data source fetch by id
-        source = self.client.get_data_source(source_id)
+        source = self.client.get_data_source(source_id)['data_source']
         self.assertEqual(source_name, source['name'])
         self.assertDictContainsSubset(source_body, source)