test: Clean up mounts in TestMachines temporary storage
test: Clean up mounts in TestMachines temporary storage

With the virsh backend there are leftover NFS mounts there. Generalize
this for robustness.

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