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
"run" is the default action for ruby blocks, and create is just an alias to that. If we think there's a downside to allowing both that is worse than forcing everyone to change existing code, then it's not difficult to add warnings for "create." If the downside of keeping both isn't that high, then "silent deprecation" (only document it as deprecated, but don't warn) seems better. Thoughts?