test: Stronger hack for rhbz#1807198
test: Stronger hack for rhbz#1807198

Ubuntu 20.04 also has libvirt 6.0.0 and thus is affected by this bug.
But restarting libvirtd causes the Machines page to not show any offline
VMs. Similar to what other tests like testNetworkSettings() do, reload
the page after restarting libvirt.

Also factorize this into a little helper function.

cockpituous/cockpit,cockpituous/cockpit,deryni/cockpit,cockpituous/cockpit,mvollmer/cockpit,deryni/cockpit,deryni/cockpit,garrett/cockpit,martinpitt/cockpit,deryni/cockpit,moraleslazaro/cockpit,deryni/cockpit,deryni/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,garrett/cockpit,garrett/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,garrett/cockpit,garrett/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,martinpitt/cockpit,deryni/cockpit,cockpit-project/cockpit,cockpituous/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit