Add some minimal debian support

This builds on PR #9 to make the module a little more debian-family friendly

* Rips out the user creation - the RH packages on yum.puppetlabs.com and the ubuntu 12.04 standard packages do this just fine.
* Only forces out an init script on RH family (yum.puppetlabs.com's 5.5 needs this still, sadly)
* Adds an `instance` parameter that's used on debian-family hosts to control which instances-enabled instance we'll be configuring/enabling.

Tested on ubuntu 12.04 and centos 6.4.