revert keeping artifacts

Keeping artifacts brings us no benefits and the produced artifacts
should never be used, because they consist of vagrant specific
settings.

For building QEMU/Virtualbox images, checkout the cloud.json file
7 jobs for master in 37 seconds (queued for 87 minutes and 7 seconds)
Status Name Job ID Coverage
  Lint
passed flake8 #2164

00:00:31

passed shellcheck #2161

00:00:37

passed shfmt #2162

00:00:25

passed validate-packer #2165

00:00:19

passed yapf #2163

00:00:31

 
  Build
failed build:qemu #2166
secure-kvm

failed build:virtualbox #2167
secure-virtualbox

 
Name Stage Failure
failed
build:virtualbox Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log
failed
build:qemu Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log