Use gerrit for python-flask-hello jobs

Change-Id: I65ede6034accaaa361e1bdea753651d059a21c1b
diff --git a/jenkins/client/job/docker/testing.yml b/jenkins/client/job/docker/testing.yml
index 147d551..c1184b6 100644
--- a/jenkins/client/job/docker/testing.yml
+++ b/jenkins/client/job/docker/testing.yml
@@ -33,7 +33,7 @@
                 default: "tcpcloud/{{name}}"
               IMAGE_GIT_URL:
                 type: string
-                default: "https://github.com/tcpcloud/python-flask-hello.git"
+                default: "${_param:jenkins_gerrit_url}/mk/python-flask-hello"
               IMAGE_BRANCH:
                 type: string
                 default: "{{branch}}"