Avoid class level variables, as they are not helpful.

Ruby 1.9.3 highlights some of the strange and confusing problems around class
level variables in Ruby; they tend to look and behave much more like global
state than people imagine, and lead down the road to trouble.

This migrates away from them to other mechanisms better fitted to solving the
problem in the Ruby language - and, typically, in ways that are much more
portable between the different Ruby interpreter implementations.

Signed-off-by: Daniel Pittman <daniel@puppetlabs.com>