Rackspace sysctl

This is an updated cookbook that follows (almost) all of the guidelines described at:
 https://github.com/rackspace-cookbooks/contributing/blob/master/CONTRIBUTING.md

Since this is my first one, I'd love some feedback. Also, I had two notes:
- LWRPs provided don't have tests (could use some guidance there)
- There's a single template that serves two purposes: a single sysctl setting in a single file, and bulk sysctl settings in a single file. I had to do some ugly hash/array repackaging to make a variable to feed to the template for both cases.

Thanks!

- Martin