[COOK-2607] Introduces chef_server_user attributes and error handling.

This merges #88 with #94 per the request at [COOK-2607](http://tickets.opscode.com/browse/COOK-2607?focusedCommentId=35970&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-35970)