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 shibumi/revert-keep-artifact in 25 seconds (queued for 1 minute and 31 seconds)
latest
Status Name Job ID Coverage
  Lint
passed flake8 #2157

00:00:21

passed shellcheck #2154

00:00:18

passed shfmt #2155

00:00:19

passed validate-packer #2158

00:00:23

passed yapf #2156

00:00:16

 
  Build
canceled build:qemu #2159
secure-kvm

canceled build:virtualbox #2160
secure-virtualbox