Reduce the number of days and artifacts to retain

Changed on these jobs:

- siab
- cord-tester (lots of pipeline jobs)
- voltha-scale

Change-Id: Ib5e2766caec22b45cd0705b8994426cd980cadb7
diff --git a/jjb/voltha-scale.yaml b/jjb/voltha-scale.yaml
index 28b274d..452059c 100644
--- a/jjb/voltha-scale.yaml
+++ b/jjb/voltha-scale.yaml
@@ -287,8 +287,8 @@
 
     properties:
       - cord-infra-properties:
-          build-days-to-keep: '{build-days-to-keep}'
-          artifact-num-to-keep: '{artifact-num-to-keep}'
+          build-days-to-keep: 30
+          artifact-num-to-keep: 15
 
     wrappers:
       - lf-infra-wrappers: