Use require_relative in puppet

Update puppet to use require_relative in cases where we know the file to load is in the same repo. This can't be used in cases where extensions may be loaded from modules, such as features, etc.

There are reports require_relative misbehaves on some versions of JRuby https://github.com/jruby/jruby/issues/5618

So we may need to implement something like what rspec did: https://github.com/rspec/rspec-support/blob/4ad8392d0787a66f9c351d9cf6c7618e18b3d0f2/lib/rspec/support.rb#L14-L31