fix copySparse for empty qcow2 disk

[vasileknik76]

Hi!

We are trying to migrate a vm for our users from qemu to vz virtualization. In our configuration we use an additional disk.

When the disk is empty and vmType is vz limactl hangs at Waiting for the essential requirement 1 of 2: "ssh".

This happens because neither write nor ftruncate is called for the file. In result after conversion, the file size is 0 bytes and the operating system cannot boot.

Steps to reproduce:

$ limactl disk create --size 1GB --format qcow2 test-disk
$ limactl start --name=test <config_file>

lima config:

vmType: "vz"
mountType: "virtiofs"
additionalDisks:
  - name: test-disk
    format: true
    fsType: "ext4"
images:
- location: "https://cloud-images.ubuntu.com/releases/22.04/release-20240308/ubuntu-22.04-server-cloudimg-amd64.img"
  arch: "x86_64"
  digest: "sha256:42dcf9757e75c3275486b397a752fb535c7cd8e5232ee5ee349554b7a55f1702"
- location: "https://cloud-images.ubuntu.com/releases/22.04/release-20240308/ubuntu-22.04-server-cloudimg-arm64.img"
  arch: "aarch64"
  digest: "sha256:0f5f68b9b74686b8a847024364031e2b95e4d3855e5177a99b33d7c55e45907f"

[AkihiroSuda]

Thanks

[vasileknik76]

Fixes #1964

[vasileknik76]

I would like to write a test for converting disks, but I haven't found a simple way to create a qcow disk from tests. Alternatively, I can embed a small disk and use it in tests. If you agree, I'll write a test

[AkihiroSuda]

Thanks, you can just exec qemu-img and call it a day for creating test disks

[vasileknik76]

I added test and installation of qemu-utils for unit tests and disabled test for windows

[vasileknik76]

@AkihiroSuda can you rerun failed tests?

[AkihiroSuda]

Thanks

[AkihiroSuda]

Thanks