Add support for airprint & printer sharing to cups cookbook

You might ask why I'm creating a pull request on a chef repo, and especially one that appears to be used by Biola University.  The reasoning is this:  it contains the only cups cookbook that I could find.

I found it useful and forked it for my own purposes to add AirPrint support.  I wanted to create this pull request in the interest of sharing changes back upstream :smile_cat:

I've added a couple features here:

 1. `cups::airprint`: Recipe to add AirPrint service definitions for sharing printers via Apple AirPrint
 2. Add `node['cups']['share_printers']` attribute (default: `true`) for configuring cupsd to share printers on local network
 3. Fixed broken `cupsd` service status detection (it was falling back to matching string `cups` in `ps -ef` output... which returned false positive: `cups-browsed`)