try this link https://ask.openstack.org/en/question/57061/hypervisorunavailable-connection-to-the-hypervisor-is-broken-on-host-compute01/ (HypervisorUnavailable: Connection to the hypervisor is broken on host)
if you running in a timeout libvirt have some trouble.
Try restart libvirt and check if the kernel module isn't in zombie state (was my problem, some weeks ago). If that just reboot your comp node