Frequently discarding old build for jobs that take up a lot of space

Change-Id: Ib3004ae6ad270648750301eb2cb8fb50b56620e2
diff --git a/jjb/defaults.yaml b/jjb/defaults.yaml
index 48174ad..4956258 100644
--- a/jjb/defaults.yaml
+++ b/jjb/defaults.yaml
@@ -34,6 +34,10 @@
     build-days-to-keep: 60
     artifact-num-to-keep: 30
 
+    # How long to keep builds and artifacts for jobs that generate a lot of artifacts
+    big-build-days-to-keep: 5
+    big-artifact-num-to-keep: 5
+
     # list of artifacts to archive
     archive-artifacts: ''