Expand environment variables in path

This should help ease the pain from
https://github.com/opscode/chef/pull/1876
until we do another chef client release
Actually, that pattern itself is probably not a good one (the gem fault-in thing in the default recipe). Do we guarantee that the default recipe gets executed? A safer thing would be to check to see if we use this gem in Chef ( believe we do), if so, then it's ok. A comment close to it might be a good way to document the assumption in that case.