Add libisoburn as dependency for xorriso

See merge request archlinux/arch-boxes!145

Remove qemu-guest-agent + removing vagrant only stuff from the cloud-image

Closes #89

See merge request archlinux/arch-boxes!142

https://github.com/archlinux/svntogit-packages/commit/6186b2ae881a762c6373f9a2497e13e27dd52bfe

cloud-init handles it + most of the "user and groups"-module options is
ignored if the user already exist.

[1] https://cloudinit.readthedocs.io/en/latest/topics/modules.html#users-and-groups

cloud-init is responsible for handling it in the cloud-image.

Fix #89

I'm not sure polkit is needed in the vagrant images, but it is
definitely not needed in the cloud-image.

It has never be enabled, makes zero sense in a cloud-image and isn't
used by vagrant.

cloud-image: Add cloud-guest-utils so cloud-init can expand the root partition

See merge request archlinux/arch-boxes!144

https://cloudinit.readthedocs.io/en/latest/topics/modules.html#growpart

Readd "remove machine-id" logic

Closes #117

See merge request archlinux/arch-boxes!141

Even though the system isn't booted, a machine-id is generated when
systemd is installed (by the .install script).

Fixes: 0b60f5a4 ("Remove "remove machine-id" logic")

Fix #117

This is helpful for checking out the results of merge requests, for instance.

change disk size 2->20GB

Closes #116

See merge request archlinux/arch-boxes!139

This also adds a snippet for always getting the most recent version of the qcow2 image.

Rename initramfs file

See merge request archlinux/arch-boxes!137

The naming scheme has changed: archlinux/archiso!74

Use tagged release as BUILD_VERSION if set

See merge request archlinux/arch-boxes!136

In my tests this gains us about 10MB.

I found that it otherwise sometimes fails to resolve in time when pacman needs it.

Use -smp 4 for qemu

See merge request archlinux/arch-boxes!129

Will more cores make the build faster? Let's find out.