Add support for defining quiet period

Change-Id: I0094118c33cd512ef04355d38482e1c91c4ee0ca
diff --git a/jenkins/files/jobs/_common.xml b/jenkins/files/jobs/_common.xml
index b255df2..975affe 100644
--- a/jenkins/files/jobs/_common.xml
+++ b/jenkins/files/jobs/_common.xml
@@ -127,6 +127,9 @@
   </properties>
   <triggers>
   </triggers>
+  {%- if job.quiet_period is defined %}
+  <quietPeriod>{{ job.quiet_period }}</quietPeriod>
+  {%- endif %}
 {#-
   vim: syntax=jinja sw=2 ts=2
 -#}