QEMU support in Packer 1.10.1 is broken (at least in the package from the offical HashiCorp Ubuntu repository)

I just installed the latest Packer 1.10.1-1 from the offical HashiCorp Ubuntu repository (https://developer.hashicorp.com/packer/install#Linux) and tried the QEMU example JSON (https://developer.hashicorp.com/packer/integrations/hashicorp/qemu/latest/components/builder/qemu):

```
$ sudo apt-get install packer=1.10.1-1
...
packer build x.json
Error: Failed to initialize build "qemu"

The builder qemu is unknown by Packer, and is likely part of a plugin that is
not installed.
You may find the needed plugin along with installation instructions documented
on the Packer integrations page.

https://developer.hashicorp.com/packer/integrations?filter=qemu
```

However, the QEMU example works fine when downgrading to 1.9.5-1:
```
$ sudo apt-get install packer=1.9.5-1
...
$ packer build x.json
Warning: Bundled plugins used

This template relies on the use of plugins bundled into the Packer binary.
The practice of bundling external plugins into Packer will be removed in an
upcoming version.

To remove this warning and ensure builds keep working you can install these
external plugins with the 'packer plugins install' command

* packer plugins install github.com/hashicorp/qemu

Alternatively, if you upgrade your templates to HCL2, you can use 'packer init'
with a 'required_plugins' block to automatically install external plugins.

You can try HCL2 by running 'packer hcl2_upgrade
/home/dreibh/src/nornet/vmimage-builder-scripts/x.json'

qemu: output will be in this color.

==> qemu: Retrieving ISO
==> qemu: Trying http://mirror.raystedman.net/centos/6/isos/x86_64/CentOS-6.9-x86_64-minimal.iso
==> qemu: Trying http://mirror.raystedman.net/centos/6/isos/x86_64/CentOS-6.9-x86_64-minimal.iso?checksum=md5%3Aaf4a1640c0c6f348c6c41f1ea9e192a2
...
```

That is, the QEMU support got broken in the 1.10.1-1 release, at least for the Ubuntu package.