additional disk configs aren't well aligned to libvirt

[cornfeedhobo]

Is your feature request related to a problem? Please describe.

libvirt assumes volumes exist only in storage pools, making :path a confusing option.

Describe the solution you'd like

Instead, :name should be exposed to users and :path should support uploading images
when the provided :path exists.

Describe alternatives you've considered

Using fog directly in the vagrantfile to prepare the storage pool. It's a difficult workaround and this is a better long term solution.