tests: don't assume eth0 network is available
tests: don't assume eth0 network is available

TestClient_UpdateNodeFromFingerprintKeepsConfig checks a test node
network interface, which is hardcoded to `eth0` and is updated
asynchronously.  This causes flakiness when eth0 isn't available.

Here, we hardcode the value to an arbitrary network interface.

hashicorp/nomad,dvusboy/nomad,hashicorp/nomad,hashicorp/nomad,burdandrei/nomad,dvusboy/nomad,hashicorp/nomad,burdandrei/nomad,burdandrei/nomad,hashicorp/nomad,dvusboy/nomad,dvusboy/nomad,dvusboy/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,dvusboy/nomad,burdandrei/nomad,hashicorp/nomad,dvusboy/nomad