Create Vagrant boxes in /tmp directory

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The easiest way to create Vagrant boxes on Ubuntu 22.04 is to create them in /tmp directory. As we're already copying QCOW image to vm.qcow2, we could copy the disk image to /tmp/x directory, do the box creation there, and then copy the resulting box back to the original directory.

We should also:

• Check the free space in the filesystem providing the /tmp path (hint: shutil.disk_usage) to ensure we don't do something stupid
• Use tarfile module to prevent unnecessary copying/renaming of disk images.