Add test coverage for Gentoo codebase

[danieldreier]

Based on issue #136 and @tampakrap's feedback on PR #140 we ought to fix Gentoo support rather than dropping it.

Gentoo Support To-Do List

• Add rspec-puppet test coverage given the facts that would be expected in a Gentoo environment
• Add a Gentoo beaker nodeset (what version(s) of Gentoo need coverage?)
• Run tests and fix the inevitable issues that are discovered
• Can we move gentoo_use and gentoo_keywords parameters from puppet::agent and puppet::server to puppet::params? I don't feel like we should have distro/OS specific parameters outside of params unless absolutely necessary. (but I don't understand what those parameters do, so that may be a bad idea)
• Add gentoo test coverage to the other puppet modules we depend on. This is a ton of work, but our ability to support a platform (and the troubleshooting effort involved in it) is massively higher when dependencies break

Anything else people can think of? I don't mean to be overly project-manager-y, just hoping that making a more specific list of tasks will make it easier to support the platform.

[tampakrap]

Regarding 2: Gentoo is a rolling distro, doesn't have versions
Regarding 4: Please drop gentoo_use and gentoo_keywords completely. It's a hack I introduced in a bunch of modules that I introduced Gentoo support. There was a discussion about this in a Puppet ticket in order to support such package specific params through a hash (BSD was also facing a similar issue)

[tampakrap]

this will help a bit #169

[danieldreier]

thanks @tampakrap, great to see movement on this.