Merge pull request #12 from mat007/clean-artifacts

Clean artefacts at the start of a Jenkins build

Author: mat007

Jenkinsfile

@@ -2,6 +2,7 @@ node('gcp-linux-worker-0') {
     stage('Build') {
         dir('src/github.com/docker/lunchbox') {
             checkout scm
+            sh 'rm -f *.tar.gz'
             sh 'docker image prune -f'
             sh 'make ci-lint'
             sh 'make ci-test'