Add Jenkins prefix url variable for running pod

Change-Id: I0ad0adaf8c501d0553a25c0384ba12d87e0de93a
Related-prod: #PROD-27737 (PROD:27737)
diff --git a/kubernetes/control/services/drivetrain/jenkins_master.yml b/kubernetes/control/services/drivetrain/jenkins_master.yml
index 3437196..60e04e3 100644
--- a/kubernetes/control/services/drivetrain/jenkins_master.yml
+++ b/kubernetes/control/services/drivetrain/jenkins_master.yml
@@ -53,6 +53,8 @@
               image: ${_param:docker_image_jenkins}
               image_pull_policy: IfNotPresent
               variables:
+                - name: JENKINS_URL_PREFIX
+                  value: "/jenkins"
                 - name: JENKINS_HOME
                   value: ${_param:jenkins_home_dir_path}
                 - name: JAVA_OPTS