Add RHEL Support

[plainprogrammer]

RHEL support requires the addition of EPEL as a Yum repository. I don't want that kind of platform specific logic baked straight in to the module since there are other things that those using EPEL probably would want to manage about that.

A way needs to be figured out to conditionally depend on a good EPEL module so that RHEL systems can be supported in a sensible way.

[plainprogrammer]

Grab this branch and run with it: https://github.com/plainprogrammer/puppet-denyhosts/tree/feature/rhel_support