Do not use cache when building flask-hello docker image

Change-Id: I15117e58b9c10835c69d292c52b08ead17edfde5
diff --git a/jenkins/client/job/docker/testing.yml b/jenkins/client/job/docker/testing.yml
index 3cdbe09..bf65dbc 100644
--- a/jenkins/client/job/docker/testing.yml
+++ b/jenkins/client/job/docker/testing.yml
@@ -39,7 +39,7 @@
                 default: "${_param:jenkins_gerrit_url}/mk/python-flask-hello"
               IMAGE_BUILD_PARAMS:
                 type: string
-                default: "--build-arg apt_repository='deb [arch=amd64] ${_param:jenkins_aptly_url}/trusty/ nightly extra' --build-arg apt_key_url=${_param:jenkins_aptly_url}/public.gpg"
+                default: "--build-arg apt_repository='deb [arch=amd64] ${_param:jenkins_aptly_url}/trusty/ nightly extra' --build-arg apt_key_url=${_param:jenkins_aptly_url}/public.gpg --no-cache"
               IMAGE_BRANCH:
                 type: string
                 default: "{{branch}}"