Change database clients to return one value and update tests

Partially implements: blueprint clients-return-one-value

Change-Id: I132115b8e9ec3859469a2b502f862c9270b17884
diff --git a/tempest/api/database/versions/test_versions.py b/tempest/api/database/versions/test_versions.py
index 37a7407..8960437 100644
--- a/tempest/api/database/versions/test_versions.py
+++ b/tempest/api/database/versions/test_versions.py
@@ -26,7 +26,7 @@
 
     @test.attr(type='smoke')
     def test_list_db_versions(self):
-        _, versions = self.client.list_db_versions()
+        versions = self.client.list_db_versions()
         self.assertTrue(len(versions) > 0, "No database versions found")
         # List of all versions should contain the current version, and there
         # should only be one 'current' version