test: Disable preloading of machines in dashboard
test: Disable preloading of machines in dashboard

Commit 313ee7ac replaced previously used "hacklib" with disabling
preloading on just the default machine. However in this test we actually
switcher between three machines quickly, which makes the issue even
worse.

Closes #13969
martinpitt/cockpit,cockpituous/cockpit,deryni/cockpit,cockpituous/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,garrett/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,deryni/cockpit,deryni/cockpit,deryni/cockpit,garrett/cockpit,mvollmer/cockpit,martinpitt/cockpit,deryni/cockpit,cockpituous/cockpit,garrett/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,mvollmer/cockpit,deryni/cockpit,moraleslazaro/cockpit,deryni/cockpit,garrett/cockpit,martinpitt/cockpit,garrett/cockpit,martinpitt/cockpit,cockpituous/cockpit,cockpituous/cockpit