Do not override database section with None

Change-Id: Ia5211718e62785d2dcebc15541fba6f054ef75b8
Related-Prod: https://mirantis.jira.com/browse/PROD-20352
diff --git a/ceilometer/server/backend/default.yml b/ceilometer/server/backend/default.yml
index 8842e11..542314c 100644
--- a/ceilometer/server/backend/default.yml
+++ b/ceilometer/server/backend/default.yml
@@ -6,7 +6,9 @@
   # they are incompatible with any legacy database publisher backends
   ceilometer:
     server:
-      database: ~
+      database:
+        engine: none
+        password: none
       publisher:
         default:
           enabled: false