Revert "libvirt: add version cap tied to gate CI testing"

This seems like it was really a policy change that should have had
more community discussion.  I think it's appropriate to revert this
now and have this as a full community discussion about options here.

This reverts commit 3bfc25a74e9dfbeb664eecf89d959428713eb178.

Change-Id: Ie19b39e99b223862ca86b9a54c5372b56e1f5d74
Merge "Revert "libvirt: add version cap tied to gate CI testing""