Fix libvirt guests

[alarmfox]

Hi,
i managed to get both guests working on a Linux host with libvirt.

General QoL 0f1f74d

I have a dedicated disks for images since my primary nvme is only 256 GB. This allows for users to specify their pool defaulting to the basic libvirt storage pool.

Windows Server 238b528

• Added authentication for winrm since the old method is not supported anymore
• Added vpindex on in hyperv_feature
• Added clock_timer -> hypervclock
• Added title for appearence in Virt Manager
• Fixed virtio-driver location in packer/templates/windows_2008_r2.json

Linux guest 60632dd

• Added metadata for libivirt provider
• Fixed "No candidate version available for docker-ce" by choosing tarball installation and version 18.06.0

[alarmfox]

Maybe this fixes #605