Add recipe with no actions, for LWRP users

We have no use for the logic inside recipes/default.rb. In fact, the logic is broken in our environment using Chef Zero, preventing our Chef runs from completing. But we have to include the ssh_known_hosts cookbook to use its LWRP.

This pull request adds a no-op recipe that may be included without performing any actions, thereby exposing the ssh_known_hosts_entry LWRP to our cookbooks.