Bug#1016028: vagrant-libvirt: allow_existing for disks is broken with recent versions of libvirt

[intrigeri]

Hi,

anonym (2022-07-25):
> The attached patch fixes this, and is in fact already merged
> upstream, but not released yet.

Update: the fix was released in 0.10.0 upstream (and 0.10.1 was
released since).

Cheers!