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)
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