Added silent_start_mode param to gating pipelines

Change-Id: I501b745406d199f8cd89efb5353393cc95a1f937
diff --git a/jenkins/client/job/gating.yml b/jenkins/client/job/gating.yml
index 1024a1e..387db35 100644
--- a/jenkins/client/job/gating.yml
+++ b/jenkins/client/job/gating.yml
@@ -35,6 +35,7 @@
                   - failed
                   - unstable
                   - not_built
+                silent_start_mode: "true"
                 event:
                   comment:
                     - added: