Remove existing warnings and run PRs through 'ruby -wc'

Puppet currently has a large number of Ruby warnings that should be cleaned up as some of them are causing actual bugs.

How to find all of the Ruby warnings in the Puppet repo (this will be slow):

find lib spec -type f -name \*.rb | xargs -n1 ruby -wc > /dev/null

After all of the warnings have been removed, we should update Travis CI to run any Ruby file changed in a PR through "ruby -wc" to make sure that we don't reintroduce any warnings (or potential bugs that would have been caught by the warnings).