Expected: your templates work.
Actual: your templates are out-of-date but it is easy to fix.
Reproducing:
$ packer build -var-file=ubuntu1804.json ubuntu.json
Error: Failed to prepare build: "qemu"
1 error occurred:
* Deprecated configuration key: 'iso_checksum_type'. Please call `packer fix`
against your template to update your template to be compatible with the current
version of Packer. Visit https://www.packer.io/docs/commands/fix/ for more
detail.
Expected: your templates work. Actual: your templates are out-of-date but it is easy to fix. Reproducing: