Icinga client (NRPE) recipe

I know you've got a separate NRPE cookbook, but I added a client recipe that includes automatic configuration of allowed_hosts via search (environment + "server_role"). It's based on the 37Signals/Opscode nagios::client recipe.

Some people like their cookbooks to provide both client- and server-side recipes. Your call on whether or not to include it :)

Tested on Ubuntu 12.04.