Fix package names and directories for Tomcat 7 on RHEL

* This builds on my colleague's earlier work on adding systemd support in #115 so merge that first.
* It closes #74. It was inspired by @joerocklin's work but I pretty much did my own thing in the end, particularly with regard to where the attributes are set.
* Using platform_family simplified some of the logic and this should close #47.
* It also closes #96, which only deals with CentOS 6 and not 7.