Updated atttribute assignment in core library to be compatible with chef 11

This wasn't working on chef-client v11.4.0 and it appears to be due to changes in the assignment of node attributes documented here:
http://wiki.opscode.com/display/chef/Breaking+Changes+in+Chef+11

This pull request updates the few places where those assignments were breaking in chef 11 - I tested against both chef 11.4.0 and 10.16.2 and it appears to work ok - I don't have an environment to perform extensive tests against this change for all the various recipe use cases.