fix tear_down from puppet_litmus

[h0tw1r3]

Summary

puppet_litmus gem is passing the target uri as the node_name param, which causes an InventoryHelper.lookup exception.

Additional Context

• Easily reproducible by following the standard litmus testing workflow with the docker, docker_exp, or vagrant backends. Provisioning and testing works fine, but litmus:tear_down throws an exception.
• By using the unnamed param to lookup instead of name, lookup will automatically search for a matching target uri, or name value.

Checklist

• 🟢 Spec tests.
• Manually verified.

[h0tw1r3]

@jordanbreen28 hotfix to #260

[jordanbreen28]

@h0tw1r3 you're on the ball 🚀