qemu output will be in this color.
==> qemu: Retrieving ISO
qemu: Error downloading: Error making HTTP GET request: 404 Not Found
==> qemu: ISO download failed.
Build 'qemu' errored: ISO download failed.
WORKAROUND
sed -Ei 's/(.*)(ubuntu-18.04.2)(.*)/\1ubuntu-18.04.4\3/' ubuntu1804.json
sed -Ei 's/("iso_checksum": ")(.*)(",)/\1e2ecdace33c939527cbc9e8d23576381c493b071107207d2040af72595f8990b\3/' ubuntu1804.json
STEPS
ACTUAL RESULTS
WORKAROUND