test: Use veth instead of assuming an eth1 in TestFirewall.testMultipleZones
test: Use veth instead of assuming an eth1 in TestFirewall.testMultipleZones

eth1 is a specific feature of our cockpit VMs, and does not exist in
e. g. the Fedora gating test VMs.

Use a veth instead, which also gets rid of the OS special cases.

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